US2450686A - Production of methyl thiophene - Google Patents

Description

Oct 5, 1948- H. E. RAsMussEN ETAL 2,450,686

PRODUCTION 0F METHYL THIPHENE Filed June 27, 1945 INVENToR ,VE/e555' 7 E. RASMUJJEA( le wLn/va c. uws/foe@ BY A ENT ofz- A oRNEY Patented Oct. A, 19.48t

UNITED STATES PATENT O FFI CIE'. 4

PRODUCTION OF METHYL THIOPHENE Herbert E. Rasmussen and Rowland C. Hansford,

Woodbury,LN. J., assignors to Socony-Vacuu'm Oil Company, Incorporated, a corporation of Applicationlune 27, 1945, Serial No.l 601,759

'l1'- Claims. 1 This invention relates to' themanufacture of alkyl derivatives of thiophene, and is more particularly concerned with a process for producing alkyl derivatives ofY thiophene' from aliphatic hydrocarbons containing ve and six' carbon atoms. Methyl thiophene and deimethyl thiophene as well `as thiophene vare well 'known compounds and occur, ordinarily, in the toluene, xyl'ene and benzene fractions, respectively, of coal tar distillates. The amounts of methyl thiophene and of dimethyl thiophene usually present inthe crude toluene and xylene fractions respectively, are of :the 'order ofabout 0.5%. The close proximityof the boil ingpoints of thiophene andbenzene, `of'methyl thiophene and toluene, and fof dimethyl thiophene and Xylene, renders the complete separation and recovery of these compounds from the corren sponding fractions, by'fracticnal distillation,v a somewhat diicult operation. Consequently, commercial benzene normallycontains traces of thiophene, and commercial toluene and xylene contain traces ofmethyl thiophene and. of dimethyl thiophene, respectively. However, since thiophene and the alkyl thiophenes are vamenable to .sulfonation much more readily than benzene, toluene and `xylen'e, thiophene and the alkyl thiophenes can be removed from` benzene, toluene and xylene in the 'formof their'sulfonates, `by repeated treatments with concentrated` sulfuric acid. This, of course, is an expensiveoperation.

Thiophene has been synthesized' inV a number of ways. In accordance with the syntheses of the prior art, acetylene has constituted a' preferred source of thiophene. Thus, it has been `proposed to VproduceV thiophene 'by reacting acetylene with pyrites, with hydrogen sulfide in the presence of catalytic material, withsulfur in thepresence or absence oi catalytic'material, and withcarbon disulde. Other' syntheses proposed have involved the reaction of lother'hydrocarbons with sulfur or hydrogen sulfide inthe presence of'various catalytic materials. Thiophene hasfrbeen 'produced also frombutyl mercaptan by dehydrogenation and cyclization, by cyclization of`other organic compounds, by interchange of heteroatoms in heterocyclicvcompounds, etc. Itl must be noted, however, that 'the yields of thi'ophene in all of these syntheses generally, havebeen'uni'- formly poor, in some cases only traces of thiophene or `derivatives thereof being produced.

The `inherent "chemical character vofithiophene and 'of alkyl derivatives of thiophene,'indicates a potentially wide use of these compounds in industrial applications; howeventhe costly nature with sulfur.

ofthe methods 'of separa'ting'and recovering'"thio-l phene and alkyl thiophenes fromcrudebenzene, toluene and xylene, and the small yields of thio' pl'xeneY obtainedl in" the proposed syntheses, have somewhat limited the use of these compounds commercially, the only present outlets of anylconsequence, being the drug and dye'elds.

Various attempts have been madeto provide cheap and commercially feasible processesA for producing thiophenmbut and as notedh'ere-in` before, processes embodying the methods known to the priorart, have suffered from two disadvantages, the first beingthe availability andconseduently,` the cost ci the charging'stocks, and' the second being the magnitude ofthe yields of thiophene achieved. Thus and as is well lknowrlto those familiar with the art, when 'the charge stock oi a given process has been readily available and its cost, therefore, has been relatively'low, the yields of thiophene have beensm'all; on the other hand, when the yields have beenhigh, the cost of the charge stock has been high.'

In the search for readily available and cheap charge stocks to synthesize organic'compounds generally, butane' and heptane have bene reacted These reactions were carriedou'tto determine what compounds would 'beforme'd and not for the express purpose Aof vsynthesizing th'io'- phene or alkyl thiophen'es. However, not more than a mere' trace of thiophene and no alkyl thiolphenes were obtained. LBaker and Reid, Jl. Am. Chem.' Soci, vol. 51, p. 1566 (1929).]

A copending application, Serial Number 601,758, iiled .lune 27, 1945, is directed to a process for manufacturing thiophene, which comprises sepa-y ratelypreheating sulfur and one' or more normal aliphatic hydrocarbons containing four carbon atoms, to temperatures such that by combining vthe preheated sulfur and the preheated'hydrocarbon material, will give a mixture having-a temperature varying between about 850i F. and about 1400o F., mixing the preheated sulfurjanid" hydrocarbon material, maintaining the temp'e'ratureof the mixture at'temperatures in excess'of about 850 i7'. for a period of 'time of at least aboutOiOl second, and reducing' the temperature'ofthe mixture to less than about 856 F. j

We have discovered that'alk'yl derivativesof thiophene may be produced insubstantial amounts, by reacting separately' preheated'aliphatic hydrocarbons containing five or. six carbon atoms, with separately preheatedsuliur'at elevated temperatures.

We 'have now found that methyl' thioph'e'ne may beobtained by reacting 'separately preheated 'aliphatio hydrocarbons containing ve carbon atoms, with separately preheated sulfur at elevated temperatures, and that dimethyl thiophene and ethyl thiophene may be obtained by reacting separately preheated aliphatic hydrocarbons containing six carbon atoms, with separately preheated sulfur at elevated temperatures.

Accordingly, it is an object of the present invention to provide a cheap process for producing alkyl derivatives of thiophene. Another object is to provide a cheap and readily available source of alkyl derivatives of thiophene.` A further object is to provide a process for producing alkyl derivatives of th-iophene that is commercially feasible. A more specific object is to provide a process for obtaining high yields of methyl thiophene, ethyl thiophene and dimethyl thiophene from aliphatic hydrocarbons containing ve and sixcarbon atoms. A very important object is to aord a process capable of carrying out the above objects by reacting separately preheated aliphatic hydrocarbons containing five and six carbon atoms, with separately preheated sulfur at elevated temperatures. Other objects and advantages of the present invention will become apparent to those skilled in the art fromthe following description taken in conjunction with the drawing, in which the single gure' represents a diagrammatic illustration of a plant for practicing the process of our invention.

Broadly stated, our invention provides a process for manufacturing alkyl derivatives of thiophene, which comprises separately p-reheating sulfur and one or more aliphatic hydrocarbons containing ve or six carbon atoms, to temperatures such that by combining the sulfur and hydrocarbon material, will give a mixture having a temperature inexcess of about 850 F., mixing the preheated sulfur and the preheated hydrocarbon material, reacting the preheated sulfur and the preheated hydrocarbon material at temperatures in excess of about 850 F. for a period of time of at least about 0.01 second, and reducing the temperature of the mixture to less than about 850 F.

A feature of the process of the present invention is that with the exception of hydrogen sulfide, alkyl thiophenes are the principal indivivdual sulfur-containing compounds obtained. A

tar, probably a mixture of complex hydrocarbon polysuldes and/or mercaptans containing about 75% sulfur is also produced. The sulfur in this tar vcan be recovered and recycled. Carbon disulfide is also formed, but only in small amounts.

The hydrogen sulfide obtained may be regenerated almost quantitatively back to sulfur for use in the process, by a very inexpensive treatment, such as incomplete combustion into water and sulfur. The sulfur in the tar may be recovered by burning the tar to produce sulfur dioxide. The sulfur dioxide can then be reacted with hydrogen sulfide to produce sulfur.

Another feature of the proces of the present invention is that the materials in the charge,

i. e., aliphatic hydrocarbons containing ve and six carbon atoms and sulfur, are cheap and plentiful.V Generally speaking, any aliphatic hydrocarbon having ve or six carbon atoms and containing at least four carbon atoms in a chain, is suitable for the process of our invention. The

Y,aliphatic hydrocarbons may be derived from any 'suitable source, as is well known in the art, and

.may consist, for example, in the production of methyl thophenc, either of pentane or iscpentane or pentenes or iscpentenes or even penta- Vunder the conditions of the process.

An important feature of our invention is that in our process the reaction is highly selective. High yields of alkyl derivatives of thiophene are obtained, and they may be recovered from the reaction product in a highly pure state using conventional and readily available fractionating equipment.

A very important feature of the present invention is that it provides a cheap and eficient method ci producing alkyl derivatives of thiophene. In our process, no catalysts are employed, thereby avoiding the disadvantages attendant on their use, suoli as regeneration and replacement problems, as well as the use of special reaction chambers. vThe process is substantially a one-step process, although as will subsequently be seen, appreciable amounts of pentenes or hexenes and of pentadienes or hexadienes may be found in the eiliuent from the reaction zone. These may be recycled to the reaction zone for further conversion into alkyl derivatives of thiophene, thereby increasing the overall yield "of the desired products. The equipment required is essentially only a pair of corrosion-resistant alloy preheaters, a corrosion-resistant alloy reactor coil and a corrosion-resistant condensing system. The separation of hydrogen sulfide presents few difficulties, since most of it can be removed by suitable stabilizing equipment and the last traces removed by caustic scrubbing or other conventional hydrogen sulde removal processes.

While relatively large quantities of sulfur are employed, it is nevertheless one of the cheapest and most non-critical chemical reagents. We have found, in the operation of our process, that the relative proportions of sulfur and hydrocarbon material may be 'varied over wide limits. However, too much sulfur results in poor efliciency in sulfur utilization per pass and favors the complete sulfurization of hydrocarbon material to carbon disulde. On the other hand, too low a proportion of sulfur lowers the conversion per pass and the ultimate yield by increasing the overall thermal degradation of hydrocarbon material. Best results are obtained using a weight ratio of sulfur to hydrocarbon material varying between about 0.5 and about 4.0, although when pentenes or pentadienes, or hexenes or hexadienes constitute the bulk of the hydrocarbon material in the charge, the lower limit of the weight ratio may be lower than 0.5.

The selectivity of the reaction involved in the process of the present invention depends primarily upon two variables, namely, the reaction `temperature at which the aliphatic hydrocarbons 'in' numerous reactions.-

we'have found that alkylvthiophenesmay-'be prozon-'some :between about 1900?' e.'andaboutziroorm Below the lower? iii-init" of the temperature range; there?- laction` isisofslow as'toi require a large .athroughput lof v.sulfur and a higher ratio :of hydrocarbon recycle for' afixed ramount of -end productgothere.- forewdetracting' from the economics o'fi'the'fop'- eration. Further, the secondary)reactionzofftar Vformation oonsumesa' largerv proportion of the charge. Above the upper 'limitl offitheztemperature'range, the secondary reaction ofdegradation of 'hydrocarbon material in` the ,chargel takes precedence, thereby'-decreas'ing 'the' yieldf-'o'f de'- rsired product. In' addition to this, high tempera'- turesffavor -the'formation' of-carbonudisulfide.: It

must fbe noted; also, that atlthese high' temperatures; corrosion problems arcata-maximum, cor- `rosion increasing perceptibly with -in cre asingftem', pera'ture,

ills-expected; We have found-that thee-optimum reaction'time'depends upon-the temperature-Jem'- ployeol. Generally speaking, other 'variables .revmaiifring consta-nt, thelower the temperature; the 'longer the reaction time. Thelreaction or'oon' tact timeY andthe -reactionitemperature :aresomewhat' fixed', one in relationto the other; by the degree ofdegradation of-'the hydrocarbon' material in the charge, and-by the eX-tent'offormation of undesirable products, which may 'be tolerated Thus, too long a contactv time at high temperatures, results in severe cracking of the 'hydrocarbon material in'the charge. The yreaction which is highly endothermic, proceeds with extreme speed. the only limitationlappare-ntly be- Ainfgfthe rapidity with whichheat-can 'be supplied to thefr'eaction' mixture. The'lower limit .of .the range ofreactiontime vis fixed, therefore; by the 'engineering problem of heat transfer and. by mechanical limitationsV such -as allowablepre'ssure drop across the reactor.' Too longareactiontime yat'temperatures in the neighborhood of Tthe lower limit of` the temperature range, vresults inlower overall yields `of alkyl thiophenes due to increased formation of heavy tar, On 'the other hand, too 'short' a reaction `time at terriperatures in 'the neighborhood of lthe lower limit of th'e'tempera- 1 ture'- ranee, results inli-ncomp'lete reaction.- Ac'- cording'ly, We have found'that for best'. results, 'the time of reaction'fis .fixed'by the reaction tem#- perature.

vIn--View of the foregoing, the :criteriato'be used 1 in'- determining optimum operating'- temperatures within the range 85'O--1300 F1, and-reactiont'imes lare` to-choo'se ther degree of'conversion desired commensuratewith'operating cost; suchas heat input and equipment costs, bearing .in `.mind that 'Within limits the `shorter the reactionv time and concordantly, the higher the temperature, the llarger the amount'of end'product which can-be realized from a unit of given' size 'per day.

Generally speaking,A the' relationship vbetween the temperature'of reaction and 'reaction timeis 'nots'ingular with our invention.- It isawellestablished yand'f'airlyfwell understood relationsliip rIn the' present instance,

-ducedby reacting'sulfur and aliphatic hydrocarbon'svcoritaining five and six'carborratomsata ltemperature falling within about 850"v F. and about' '1'300 FL, for a period of time selected'to minimize'the-yields of secondary reactionprod- 'ucts`v at the selected temperature. Accordingly, for the reaction temperaturer'angeof ourfprocess, i.- er, 850 F; to '1300"' E., when foperatingicontinulouslyiwithareactorA coil lof .sutable'sizelandlatia practicaiicharg-e rate., we have'cfoundithat'the low- CII est practical liinitv of-stheiitime zo'fireactioniisiofnthe order ofl10.01 secori'dat aboutrlgoofi: 'Theupper practical limit: .of "reactionrtime, other variables remainingxconstant', willfcorrespond 'toflthe' lower 'limit'.xof. :the temperature 1 of.` reactionzand' may i'be offthei orderzof :several seconds; i

. Separate` preheating. of; :the 'hydrocarhon.- .rerka'ctant anda-sulfur, and .quenchingrofathe reaction mixture are necessary for vac'hi'e'aying.the.some- Whazticlo'seioontrol of thelreactionrtimeiata given reaction temperature.- This 4'is Veryfimportant 'fin Atltefspecilicreaction producing. methyl fthiophene yor fdimethylr' `thiophene andv ethyl- '.thi'oph'ene.` Without A.fany intention fof limiting the lscope of therpresentsinvention, itis .suspectedfthatza riuniflber'soffreactions '.occuriin-the 'reaction between :the Ihydrocarb-on'.freacitant andlsulfiur.' Inthis con znection; the' following should Aloe :noted: cracking `ofratl-re;'hydrocarboni:reactan't"destroying:'.tloefffour ori-more'. :carbon-atom vstraight-chain Astructure (the-fourztearbonaatom .straieht-.chain structure beinga; prerequisiteifor theformation o'fl the thiophenenucfleus) V; 'formation .of tarrhigh'fi-nsulfur.; :formation .ofthe thiopherre nucelus and formation ofxcarbon disulfide.: These reactionsicompetefwithroneianother.' We .haye'ffound' that-.the .rates "of 'the'.L formation f vof lighter `iliydrocarbons and of the formation of carbon disulfideare 'some'- what slowerfthan thatrrequiredforthe formation `:of-tizie:tl'ii'opl'iene'- nucleus; Accordingly; sa l proper fcontrro'l of 'the reaction time ata givenreaction Jtern-perature aci'i-i'evede by/ separateprehea'ti-ng, mixing, heating .'at'l'awgiven `temperature'ifor la cor- :responding period` fof' time, and'. quenching -is v-pheneror:dimethyl.'thiophene' and Eethyl flthiop'hene withrlimitedtyi'elds of earb'on disulfide y.and lfixed gaseslclueito. .a' limited'. 'decomposition' of the hy- Adrocarbon reactant, 'The'ratef'ofthebreaction'pro- :ducine'ltar fis ifairly'zcioseito' thatA rerpiirodl 'for'- the formation of the"thiophen'e'l nucleus and@ therefore; .the control `of this reaction is :more 'difficult .;Hence.,l ,'inespite ofi the" separate fprehea'tin'gzand ultimate .quenchingl of .the reaction' mixture', the yields` .of tar "approximate :those A of yn-iethylthiophene' or oflfdimethylithiophenelandLethyl -th-io'- pl'ifene'.. n

.In fcarryingout vrthe..process--of thepresent inyention, :therefore it' fis; essential. to'"separately `preheat the reactants; Heatin'gfth'e hydrocarbon material 'and 'the'- sulfur. together. has 'two'iundesirable effects.; Inxtherstplace; at11oWer1temyperat'ur-es, :the'irea'ct-ion; producing tar i formation is :the favored reaction; .and`.in.the second 'pla'ce, theseheavy. products -are subsequently cracked "in th'etrea'ctorv at' the: selected'treacticn tempera-ture, causing. undue' coking.'y Tests have' shown' that .When/.ther reactants are'. heated' togetherriup to temperatureswithin 'the' aforementioned .reaction t'emperature'range, 'tar formationua-lways results, and? in 'such quantities, .that the reaction icone' :is eventually plugged :up :with ya heavy,V carbona'ceous deposit.. Accortimely,v itisiessential :in-our process to separately preheatseach iof the '-'re'a'ctants, xi.' e., thefhydrocarbon orrth'e ymixturefofhydrocarbons 'constitutingcthe hydrocarbon rea-etant andxsulfur.; toffsuch .tempera-tures thatfi when'. ythey are brought;l together, under-.g 'properf A.conditions '-,of flow, a temperature fallingA within thenreacton .temperature range-isi achieved, before effecting contact;r betweenv` them. :In practice,` this' is.4 effected; ordinarily,A :byf` yseparately preheating.; each ofi the: reactantsI toV :temperatures: within'. the reaction temperature range.

After-thetseparatelw :prehcateof hydrocarbon 'adsense reactant and sulfur are mixed and allowed to react for the reaction time indicated by the operating temperature, the temperature of the reaction mixture is immediately lowered to Vbelovv about 850 F., in practice, appreciably below 850 F., in order to avoid overreaction in the system after leaving the reactor. This may be accomplished suitably by spraying the eflluent of the reactor with aliquid.

As stated hereinbefore, for economical operation of the process, we prefer not to use a hydrocarbon charge consisting predominantly of pentadiene or hexadiene, because of their tendency to polymerize in the preheater with consequent cracking and severe coking in the reactor. However, when pentadiene or Vhexadiene are used in conjunction with predominant amounts of pentanes and/or pentenes, or with predominant amounts of hexanes and/or hexenes, respectively, or suitable diluents which are inert with respect to sulfur and to other reaction products yof the process, for example, nitrogen, carbon disulfide, carbon dioxide, etc., they can be processed satisfactori-ly to give high yields of alkyl derivatives of thiophene. process, we have found that pentadienes or hexadienes should constitute a minor proportion of the charge.

In our process, the reaction is effected, preferably, at atmospheric pressure or under sufficient pressure to cause the flow of the reactants through the reactor andauxiliary system, under the desired reaction conditions. Tests have shown that the yields per pass and ultimate yields of methyl thiophene or dimethyl thiophene and ethyl thiophene decrease with increase in pressure. However, even at appreciable pressures, methyl thiophene or dimethyl thiophene and ethyl thiophene are nevertheless produced in substantial amounts. Accordingly, there appears to be nothing critical about pressure as a reaction variable. We have found that best results are obtained when turbulent flow is maintained through the reactor, suitably, a conventional coiltype pipe reactor. With this type of reactor, the desired turbulent flow may be achieved with a pressure drop of about 1 to 20 pounds across the coil, depending upon the size of the pipe and the length of the coil. Turbulent flow promotes heat transfer and assures good mixing of the reacting .vapors of sulfur and hydrocarbon material.

Recycling of the unreacted portionof hydrocarbon material in the eiiiuent stream, has been found to be a desirable scheme for increasing the ultimate yield of desired product. This has the same eiect as lengthening the reactionv time without the attendant and undesirable degradation of hydrocarbon material, referred to hereinbefore. When the parafiinic hydrocarbons are the hydrocarbon reactants, it is suspected that the reaction proceeds stepwise with the formation of the corresponding oleflnic hydrocarbons, diolelnic hydrocarbons and finally, alkyl thiophenes, each step causing the formation, simultaneously, of hydrogen sulfide, molecular weight for molecular weight. These reactions occur concurrently and unreacted pentane or hexane as well as pentenes or hexenes and pentadienes or hexadienes are found in the effluent. Only traces of acetylenic hydrocarbons have been found. The hydrocarbons in the eiiluent serve as recycle stream in the recycling operation. In this connection, it must be observed that when pentenes or hexenes are the sole constituents ofthe hydrocarbon reactant, recycling of the hydrocarbons in the effluent For eifective operation of our naces, as shown,

is not commercially feasible in View of the high concentration of pentadienes or hexadienes, `respectively, in the recycle stock. However, and as stated hereinbefore, pentanes or hexanes, or other suitable diluents may be added to the recycle stocks and the latter processed to give high yields of alkyl derivatives of thiophene.

Accordingly, a most important feature of our process, is that it is flexible, it being possible to produce pentenes or hexenes as well as pentadienes or hexadienes from pcntane or hexane, or pent'adienes or hexadienes from pentenes or hexenes, respectively, in addition to alkyl thiophenes.

A plant for practicing the process of our invention with respect to the manufacture of methyl thiophene is illustrated diagrammatlcally in the drawing. It is understood, of course, that certain modifications of this operating scheme, as well as changes in the type of equipment employed, may be made as long as the essential requirements of the process are maintained, as Will be obvious to those skilled in the art, once'the conditions of the process, with which this invention is concerned, are clearly understood.

Referring now more particularly to the drawing, pentane is pumped from a storage sphere 4 by a pump 5, to a preheater coil 6. Molten sulfur is pumped from a storage tank I by a pump 2, to a preheater coil 3. The preheated vapors of pentane and sulfur are mixed at a point 'l prior to introduction into the reactor, and are then sent through a reactor coil 8. The preheaters 3 and B and the reactor 8 ymay each be in separate furnaces if desired, or, if in the same furmay be of different lengths to produce the desired preheating temperatures and reaction temperatures. As stated hereinbefore, for economical operation of the process of the present invention, short reaction times must be used. This requires rapid mixing of the reactants and rapid heat transfer to the reaction mixture. The reaction products enter a spray .chamber 9 Where they are quenched to a temperature of about 300 F., by spraying suitably with crude methyl thiophene or some other liquid product of the process. The quenched reaction products subsequently are passed into a tar-separator l0, wherein tar separates out and is sent to a sulfur-recovery plant I9. The reaction products free of the bulk of the tar, go to a filter H, to separate the tar mist. A Cottrell precipitator may be used as the mist collector if desired. The filtered products are then passed into a condensate stripper column I2 where most of the products that are normally liquid are stripped out. This column may be operated as an absorption stripper by using methyl thiopene bottoms as the absorber liquid. The overhead from the condensate stripper column l2, go to a compressor I3 and thence to a column I4 where Ca-hydrocarbon gases, gases lighter than Cahydrocarbons, and hydrogen sulfide are removed as overhead and sent to the sulfur-recovery plant I9. The bottoms from the column I4, consisting of Cr-hydrocarbons and materials having boiling points higher than Cri-hydrocarbons, are -passed into a column l5 Where (D4-hydrocarbons are obtained as overhead. The bottoms from column I5, consisting of Ce-hydrocarbons and materials having boiling points higher than C5- hydrocarbons together with the liquid bottoms from the condensate stripper vcolumn I2 are passed into a column 20 where C-t-hydrocarbons are obtained as overhead, combined with the overhead from the debutanizer column l5,

and `recirculated 'through a meter I6 to .the preheater V(i, and thusreturned to the process as recycle stock. The -bottoms from the column '20 are sent ato the :carbon disulfide tower I'I. -Ca-rbon Vdisulfide taken off as overhead from `the tower Il' and sent to storage, While the bottoms from the tower "I1 are passed into a vthiophene tower I 8 where thiophen'e produced as a result of some cracking of (Z5-hydrocarbons `into C4- hydrocarbons, is taken as overhead and lto storage. The thiophene tower bottoms are passed into `amethyl .thiophene tower I9 where `methyl thiophene is Vtaken as overhead and to storage andmethyl thiophene tower bottoms taken to storage to be used the condensate lstripper column I2 and/or Vas a spray .in the spray'chamber 9.

.In a. typical operation, the hydrocarbon mateterial charged to the preheated coil 6 is made up of a normal pentane cut containing varying amounts of pentenes, obtained from a cracking unit for the conversion of gas oil into gasoline. Sulfur is vcharged to thepreheater 3, in amounts to produce a mixture vat 'I having a weight ratio of sulfur to butane zout, of about 1.0 and the charge rates are adjusted to give a reaction time of about 0.06 second in the reactor coil 8 at temperatures of -1100F.

The following detailed examples are for the purpose of illustrating modes of producing' alkyl thiophenes in accordance with our invention, it fbeing clearly understood that the invention is not Ato Abe vconsidered as limited to the specific manipulations and conditions set forth hereinafter.

Eawunpler 1 834 grams of isopentane were charged into a preheater at the rate oi 40 grams per minute and heated to a temperature of '1080 F. 583 grams ofv sulfur were charged to a separate preheater at a rate of 28 grams per minute' and heated to a ,temperature of 10801F. The two streams were sentthrough a m-ixing nozzle and thence through a baiiled'tube reactor of 50 cc. volume constructed of 27% chromiumstainless steel maintained at a temperature of'1200,F. The reaction product was 'quenched with'a water spray, passed through afsmall Cottrell precipitator to remove tar mist, and scrubbed through a hot countercurrent caustic tower. The liquid product was cooled, condensedand separated in a Water cooler and ice trap. 7.53 grams of liquid were recovered. Fractionation ofthe liquid through a I 5 theoretical-plate column gave 88 grams of a product having `a boiling range o'fV 10'7-115 C'. Bhysical measurements and chemical testsestablished. this fraction to be methyl thiophene.

Example 2' spirit. yor essential..v attributes thereof, and .itis

therefore desired that the present embodiments be considered in all respects as illustrative and not restrictive, reference being had to the appended claims rather than to the foregoing description to indicate vthe scope of the invention.

We claim:

l. A process for producing methyl thiophenel which comprises separately preheating sulfur and a hydrocarbon selected from the group consisting ofvpentanes, pentenes, and pentadienes, havin gat leastfour carbon atoms in a straight chain, te temperatures such that combining said sulfur and said hydrocarbon will give a reaction mixturehaving a temperature varying between about 8509 F. anduabout 1300" F.; mixing the preheated sulfur and the preheated hydrocarbon; reacting said vpreheated sulfur with said preheated hydrocarbon at a reaction ytemperature vvarying between y550 lF. and about 1300 F., to aproduce a methyl thiophene-containing mixture; and reducing thetemperatureiof said methyl thiophenecontaining mixture to less than 850 F.

v2. A process for lproducing methyl thiophene, which comprises separately preheating sulfur and a pentane having at least four carbon atoms in a straight chain, to Ytemperatures such that combining said sulfur and said pentane will give a reaction mixture having a temperature varying between about-900 F. and about 1100 F.; mixing the preheated sulfur and the preheated pentane; reacting said preheated sulfur with said preheated pentane at a reaction temperature varying 'between about 900 F. and about 1100 F. for a pe-; riod of time selected to yminimize the yields of hydrocarbons containing less than four `carbon atoms per molecule and carbon clisulde at said reaction temperature, to produce a methyl 'thiophene-containing mixture; and-reducing thetemperature of said methyl thiophene-containing mixture to less than about 850 F.

3. A process for producing lmethyl thiophene, which comprises separately preheating sulfur anda pentene having at least fourcarbonatoms in a straight chain, to temperatures such that combining-said-sulfur and said pentene will give-n a reaction mixture having a temperature varying between vabout 900 F. and about 1100 F.;-

mixing the preheated-sulfur vand the preheated` pentene; reacting said preheated sulfur with-said preheated pentene at a reaction temperature varying ybetween about 900 F. and about 1100 F. for a period of time selected tominimize the yields-.of yhydrocarbons containing less than four carbon atoms per molecule and carbon disulde atsaid reaction temperature, to produce a methyl thiophene-containing mixture; and reducing the temperature of said-methyl thiophene containing mixture to less than about 850 F.

,4. A process for producing vmethyl thiophene, which comprisesl separately preheating. sulfur and a hydrocarbon mixture containing a minor pro.- portion of apentadiene having at least four carbon atoms in a straight chain, to temperatures such that combining said sulfurand said hydro-- carbon mixture will givea reaction-mixture havinga temperature varying Abetween about 900 Fand about 1100 F.;-,mixing Vthe preheatedsuliur. and .the .preheated hydrocarbon mixture; reacting ysaid preheated sulfur with said preheated hydrocarbon -mixture ata reaction .temperature varying between about 900'` F. and about .1100 F. -ior a period of ytime selectedto minimize .the yields of hydrocarbons containinaless than four carbonatoms per molecule-.andlcarbon-disuliide at saidreacton temperature, to producev a methyl thiophene-containing mixture; and reducing the temperature of said methyl thiophene-containing mixture to less than about 850 F. Y

5. A process for producing methyl thiophene, which comprises separately preheating sulfur and a hydrocarbon selected from the group consisting of pentanes, pentenes, and pentadienes, having at least four carbon atoms in a straight chain, to temperatures such that combining said sulfur and said hydrocarbon will give a reaction mixture having a temperature varying between about 900 F. and about l100 F.; mixing the preheated sulfur and the preheated hydrocarbon; reacting said preheated sulfur with said preheated hydrocarbonl at a reaction temperature varying between about 900 F. and about 1100 F. to produce a methyl thiophene-containing mixture; and reducing the temperature of said methyl thiophenecontaining mixture to less than about 850 F.

6. A process for producing methyl thiophene, which comprises separately preheating sulfur and a pentane, having at least four carbon atoms in a straight chain, to temperatures such that combining said sulfur and said pentane will give a reaction mixture having a temperature varying between about 850 F. and about 1300 F.; mixing the preheated sulfur and the preheated pentane; reacting said preheatedsulfur with said preheated pentane at a reaction temperature varying between 850 F. and about 1300 F. for a period of time selected to minimize the yields of hydrocarbons containing less than four carbon atoms per molecule and carbon disulfide at said reaction temperature, to produce a methyl thiophene-containing mixture; and reducing the temperature of said methyl thiophene-containing mixture to less than 850 F.

7. The process which comprises separately preheating sulfur and a pentane having at least four carbon atoms in a straight chain, to temperatures such that combining said sulfur and said pentane will give a reaction mixture having a temperature varying between about 850 F. and about 1300 F.; mixing the'preheated sulfur and the preheated pentane; reacting said preheated sulfur with said preheated pentane at a reaction temperature varying between 850 F. and about 1300 F. for a period of time selected to minimize the yields of hydrocarbons containing less than four carbon atoms per molecule and carbon disulde at said reaction temperature, to yield a product containing thiophene, methyl triophene, normal butane, normal butenes, butadienes, and pentanes, pentenes and pentadienes, containing at least four carbon atoms in a straight chain; reducing the temperature of said product to less than 850 F.; separating normal butane, normal butenes, butadienes, and pentanes, pentenes and pentadlenes, containing at least four carbon atoms in a straight chain from said product; and recycling said normal butane, normal butenes, butadienes, and pentanes, pentenes and pentadienes, containing at least four carbon atoms in a straight chain to the process.

8. A process for producing methyl thiophene, which comprises separately preheating sulfur and a pentene having at least four carbon atoms in a straight chain, to temperatures such that combining said sulfur and said pentene will give F a reaction mixture having a temperature varying between about 850 F. and about 1300 F.; mixing the preheated sulfur andthe preheated pentene; reacting said preheated sulfur with said preheated pentene at a reaction temperature varying between 850 F. and about 1300`F. for a period of time selected to minimize the yields of hydrocarbons containing less than four carbon atoms per molecule and carbon disulfide at said reaction temperature, to produce a methyl thiophene-containing mixture; and reducing the temperature of said methyl thiophene-containing mixture to less than 850 F. y

9. The process which comprises separately preheating sulfur and a pentene having at least four carbon atoms in a straight chain, to temperatures such that combining said sulfur and said pentene will give a reaction mixture having a tmperature varying between about 850 F. and about l300 F.; mixing the preheated sulfur and the preheated pentene; reacting said preheated sulfur with said preheated pentene at a reaction temperature varying between 850 F. and about l300 F. for a period of time selected to minimize the yields ci hydrocarbons containing less than four carbon atoms per molecule and carbon disulfide at said reaction temperature, to yield a product containing thiophene, methyl thiophene, normal butane, normal butenes, butadienes, and pentanes, pentenes and pentadienes, containing at least four carbon atoms in a straight chain; reducing the temperature of said product to less than 850 F.; separating normal butane, normal butenes, butadienes, and pentanes, pentenes and pentadienes, containing at least four carbon atoms in a straight chain from said product; and recycling said normal butane, normal butenes, butadienes, and pentanes, pentenes and pentadienes, containing at least four carbon atoms in a straight chain to the process.

l0. A process for producing methyl thiophene, which comprises separately preheating sulfur and a hydrocarbon mixture containing a minor proportion of a pentadiene having at least four carbon atoms in a straight chain, to temperatures such that combining said sulfur and said hydrocarbon mixture will `give a reaction mixture having a temperature varying between about 850 F. and about 1300 F.; mixing the preheated sulfur and the preheated hydrocarbon mixture; reacting said preheated sulfur with said preheated hydrocarbon mixture at a reaction temperature varying between 850 F. and about 1300 F. for a period of time selected to minimize the yields of hydrocarbons containing less than four carbon atoms per molecule and carbon disulfide at said reaction temperature, to produce a methyl thiophene-containing mixture; and reducing the temperature of said methyl thiophene-containing mixture to less than 850 F.

l1. The process which comprises separately preheating sulfur and a hydrocarbon mixture containing a minor proportion of a pentadiene having at least four carbon atoms in a straight chain, to temperatures such that combining said sulfur 'and said hydrocarbon mixture will give a reaction mixture having a temperature varying between about 850 F. and about 1300 F.; mixing the preheated sulfur and the preheated hydrocarbon mixture; reacting said preheated suliur with said preheated hydrocarbon mixture -at a reaction temperature varying between 850 F. and about 1800 F. for a period of time selected to minimize the yields of hydrocarbons containing less than four carbon atoms per molecule and carbon disulfide at said reaction temperature, to yield a product containing thiophene, methyl thiophene, normal butane, normal butenes, butadienes, and pentanes, pentenes and pentadienes, containing at least four carbon atoms in a straight chain; reducing the temperature of said product to less than 850 F.; separating normal butane, normal butenes, butadienes, and pentanes, pentenes and pentadienes, containing at least four carbon atoms in a straight chain from said product; and recycling said normal butane, normal butenes, butadienes, and pentanes, pentenes and pentadienes, containing at least four carbon atoms in a straight chain to the process.

HERBERT E. RASMUSSEN.

ROWLAND C. I-LANSFORD.

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

UNITED STATES PATIENTS Number Name Date 1,907,274 Wheeler et al May 2, 1933 5 2,389,215 Singleton Nov. 20, 1945 2,410,401 Coffman Oct. 29, 1946 2,411,236 Thacker Nov. 19, 1946 OTHER REFERENCES 10 Shepard, J. Am. Chem. Soc. 56, 1355-6 (1934).

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