US2450659A - Sulfur and hydrocarbon reactions and products - Google Patents

Description

Oct- 5, 1948 R. c. HANSFORD ETAL 2,450,559

SULFUR AND HYDROCARBON REACTIONS AND PRODUCTS Filed Aug. 27, 1946 3 Sheets-Shea?l 1 and ALEXANDER M 9CH/4NI INVENTORS ATTORNEY UCL 5, 1948- R. c. HANsFoRD ET AL 2,450,659

SULFUR AND HYDROCARBON REACTIONS AND PRODUCTS Patented Oct. 5, i948 SULFUR AND HYDROCARBON REACTIONS AND PRODUCTS Rowland C. Hansi'ord, Herbert E. Rasmussen,

and Alexander N. Sachanen, Woodbury, N. J., assignors to Socony-Vacuum Oil Company, Incorporated, a corporation of New York Application Aug-ust 27, 1946,

Serial No. 693.176

In Great Britain November 29, 1945 This invention relates to the manufacture of organic compounds, and is more particularly concerned with a process for producing butadiene,

thiophene, and certain derivatives of thiophene from normal aliphatic hydrocarbons containing four carbon atoms.

Butadiene is a well known compound and, in

general, is a synthetic product. It is a valuable hydrocarbon useful in numerous organic syntheses, and particularly important as an intermediate'in the manufacture of synthetic rubber. The prior art on the conversion of hydrocarbons to butadiene is rather large and embraces a variety of reactions. In most instances, monooleiinic hydrocarbons are the preferred starting materials. However, in many cases, a two-step process is involved wherein a paralnic hydrocarbon, such as butane, is dehydrogenated -to a monooleflnic hydrocarbon, such as butene, in the rst stage, and subsequently, the monoolenic hydrocarbon is dehydrogenated to a diolenic hydrocarbon, such as butadiene, in the second stage.

Claims. (Cl. 260-329) step; Thus, United States Patent No; 2,224,155 discloses a process for converting butane to butadiene in the presence oi chlorine with Afused molten metal chlorides as catalysts. British Patent No. 524,918 and French Patent No. 853,646. describe the conversion of butane to butadiene at temperatures of 50o-'100 C. in the presence of a catalyst comprising at least 50 per cent zinc oxidc in admixture with other metal oxides or salts.

The use of typical dehydrogenation catalysts of the chromium oxide type, for example, necessitates a two-step process, since the conditions for the formation of a monoolenic hydrocarbon ,i from a parainic hydrocarbon are quite different from those required for the conversion of a monoolenic hydrocarbon to the corresponding dioleiinichydrocarbon in the presence of thistype of catalyst.' Higher temperatures, greatly reduced pressures, and shorter contact times are optimum for the latter conversion.

The disadvantages of two-stage processes are obvious when it is-considered that the monoolenic hydrocarbon must be separated from the first stage 'for processing in the second stage.

Conversions per pass usually are kept low in order to avoid secondary reactions such as cracking,

`withresult'ant carbon and light gas formation.l

Theuse of catalysts entails, of course, periodic regeneration which involves high initial and operation costs. y

Some processes have been proposed, however,

whereby butane is converted to butadiene in one However, the relatively high cost of the catalysts involved in these processes due either to the nature of the catalyst itself or to the relatively large amounts employed, has rendered the utility of these processes somewhat questionable from the standpoint of commercial feasibility.

Thiophene likewise is a welll known organic compound and occurs, ordinarily, in the benzene fraction of coal tar distillates. The amounts of thiophene, usually present in the crude benzene fraction, are of the order of about 0.5%. The close proximity of the boiling points of thiophene and benzene renders the complete separation. and recovery of thiophene from the benzene iraction, by fractional distillation, a somewhat I, H1 cult operation. Consequently, commercial benzene normally contains traces of thiophene. However, since thiophene is amenable to sulfonation much more readily than benzene, thiophene can be removed from benzene in the form of its sulfonate, by repeated treatmentswith concentrated sulfuric acid. This, of course,` is an expensive operation.

Thiophene has been synthesized in 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 produce thiophene by reacting acetylene with pyrites, with hydrogen suluflde in the presence of catalytic material, with sulfur in the presence or absence' of catalytic material, and with carbon disulde. Other syntheses proposed have involved thereaction of other hydrocarbons with sulfur or hydrogen sulfide in the presence oi'.

various catalytic materials. Thiophene has been ering thiophene from crude benzene and the small yields obtained in the proposed syntheses, re-

' ferred to hereinbefore, have somewhat limited the use of this compound commercially, the only present outlets of any consequence being the drug and dye fields.

Various attempts have been made to provide cheap and commercially feasible processes for producing thiophene; but as noted hereinbefore, processes embodying the methods known to the prior` art have suffered from two disadvantages, the first being the availability and consequently, the cost of the charging stocks, and the second being the magnitude of the yields ofy thiophene achieved. Thus, and as is well known to those familiar with the art, when the chargefstock of a given process has been readily available and its cost, therefore, has been relatively low, the yields of thiophene have been small; on the other hand,-

When the yields have been high, the cost of the charge stock has been high.

In the search forreadily available and cheap charge stocks to synthesize organic compounds generally, butane has been reacted with sulfur. This reaction Was carried out to determine what compounds would be formed and not for the express purpose of synthesizing thiophene or butadiene. However, not more than a mere trace of thiophene and no-butadiene were reported. [Baker and Reid, Jl. Am. Chem. Soc., vol. 51, page 1566 (1929).]

We have discovered that thiophene, certain thiophene derivatives and butadiene maybe produced in substantial amounts, by reacting separately preheated normal aliphatic hydrocarbons, containing four carbonatoms per molecule, with separately preheated sulfur, at Yelevated temperatures.

Accordingly, it is an object of the present in` vention to provide a process for manufacturing organic compounds. Another object is to provide a cheap and readily `available source of thiophene, butadiene andA certain derivatives of thiophene. A further object is to provide a cheap process for producing thiophene, butadiene and certain derivatives of thiophene which is commercially feasible. A more specific object is to provide a process for obtaining high yields of thiopheneand butadiene from normal aliphatic hydrocarbons containing four carbon atoms per molecule. A very important object is to aiford` a process capable of carrying out the above objects by reactingv separately preheated normal aliphatic hydrocarbons containing four car-bon atoms per molecule, with separately preheated sulfur, at elevated temperatures.

Other objects and advantages of the present invention will become apparent to those skilled to those of thiophene.

I and the reaction temperature;

thiophene and the charge; i

Figure 2 shows a curve representing graphically the relationship between the sulfur through-put Figure 3 shows a. curve representing graphically the relationship between the ultimate yield of thiophene in recycle operation, and the reaction temperature;

vFigure 4 shows a curve representing graphically the relationship between the yield per pass of thi ophene and the reaction temperature; and

Figure 5 is a diagrammatic illustration of a plant for practicing the process of our invention.

Broadly stated, our invention provides a process for manufacturing thiophene, thiophene derivatives, and butadiene, which comprises sepv arately preheating sulfur and one or more normal aliphatic hydrocarbons selected from the group consisting of normal butane and normal butenes (butadienes lmay also be used in the charge when thiophene is the iinall product of the process),y

to temperatures such that combining the sulfur and hydrocarbon material will give a. mixture having a temperature in excess of about 850 F.,

mixing4 the preheated sulfur and preheated hydrocarbon material, maintaining the temperature of the mixture at temperatures in excess oi' about 850 F. for a period of time sufficient to produce the desired products, and reducing the temperature of the mixture to less than about 850 F.

A feature of the process of the present invention is that withvthe exception of hydrogen sulfide and a tar, thiophene or butadiene are the principal compounds obtained. Carbon disulfide is also formed, but only in small amounts. The hydrogen sulfide produced may be regenerated almost quantitatively back to sulfur for use in the process by an inexpensive treatment, such as incomplete combustion into water an-d sulfur. The tar is obtained in amounts which are about equal Certain useful products may be obtained from this tar, for example, mei'- capto-thiophenes and other heavier derivatives of thiophene. The balance of the tar or tar residue, containing about 75% of sulfur, may be processed for the recovery of sulfur which can then be recycled to the process. Thus, the sulfur in the tar residue may be recovered by burning the Presidue to produce sulfur dioxide. The sulfur dioxide can then be reacted with hydrogen sulde the normal aliphatic hydrocarbons represented by the molecularl formulas 04H10, C4Ha and Cil-Is,- the latter being used when thiophene is the nal in the art from the following description .taken which: y

Figure 1 shows va. curve representing graphically in conjunction with the following drawings, in

product of the process. These aliphaticl hydro? carbons may be derived from any suitable source, as is well known in the art, and may consist either of normal butane or normal buten'es or mixtures of them, or even butadienes or mixtures of butadienes with normal butane and/or normal butenes v d when the process is operated to produce thiophene. It should be observed, however, that for yeconomical operation of our process, when thiopheneis thedesired end-product, itis notv preferred to use a hydrocarbon chargeconsistingprev dominantly of butadienes because of their tenden'cy to-'polymerize'` under the conditions of 'the process. vA conventional source of normal butane 1 proportion of sulfur inthe Generally speaking, the ali-- A and normal butenes is the gases obtained around in our process the reaction is highly selective.

High yields of thiophene or of butadiene are obtained, and they may be recovered from the reaction product in a highly pure state usingconventional and readily available equipment.

A very important feature of the present invention is that it provides a cheap and eillcientv method of producing Ythiophene or butadiene. In our process, no .catalysts are employed, thereby avoiding the disadvantages attendant on their use, such as regeneration and replacement problems, as well as the use of special reaction chambers. The process is substantially a one-step process. In operation, appreciable amounts of butenes (and butadienes, when the process is operated to produce thiophene) will be found in the eilluent from the reaction zone. 'These may be recycled to the reaction zone for further conversion into butadiene or thiophene, thereby increasing the overall yield of the desired product. The equipment required is essentially only a pair of corrosion-resistant alloy preheaters, a corrosion-resistant alloy reactor coil and a corrosionresistant recovery system, The separation of hydrogen sulfide presents few dileulties, since most of it can be removed by suitable pressure fractionation equipment and the last traces removed by caustic scrubbing or other conventional hydrogen sulfide 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, and as shown in Figure 1 and in Examples 1, 2, 3 and 4, that the relative proportions of sulfur and hydrocarbo material in the charge may be varied over wide limits.

The data presented in Figures 1, 2, 3 and 4, were obtained by pumping normal butane through a hydrocarbon preheater at a rate of 31A grams per minute. The preheater coil consisted of 20 feet of 0.15-inch internal diameter, 18-8 stainless steel tubing, immerse-d in a lead bath kept at various temperatures. Molten sulfur was pumped at various rates through a preheater ccil consisting of 20 feet of 1/-inch iron pipe size, 27% chromium stainless steel tubing, immersed in a lead bath kept at various temperatures. The preheated reactants were then sent through a mixing nozzle and then through a reactor consisting of 12 feetof 1/-inch iron pipe size, 27% chromium stainless steel tubing immersed ln a lead bath kept at various temperatures. The pressure drop across the reactor was about 12 pounds per square inch gauge, and the reaction time was about 0.07 second. The reaction product was quenched with a Water spray to arrest further reaction. The quenching operation resulted in a separation of the reaction mixture into essentially two fractions, one a relatively non-volatile tar and the other the more volatile constituents comprising light hydrocarbon gases, including butadiene, bu-

tenes and unreacted butane: and vaporiaed sulfur compounds, including carbon disulfide and thiophene. The latter fraction was sent through water-cooled heat exchangers to a tar trap, and thence to a glass. wool illter .where the entrained tar mist was filtered out. The ultered vapors were subsequently sent through a countercurrent caustic scrubber maintained at a temperature of about 176 F. for the removal of hydrogen sulde. The remaining vaporous reaction product stream was sent through an efllcient cooling system and finally to an ice trap for collecting the crude thiophene. The olif-gases from the ice trap were metered andsamples thereof subjected to Podbielniak distillation. In those runs where recycle was used (Figures 2 and 3), the off-gases werecom pressed and liqueued and after bleeding of! the light gases, were recycled to the hydrocarbon preheater.

Within rather wide limits of sulfur concentration, the selective conversion to butadiene or thiophene is substantially the same, although the conversion per passis directly proportional to the amount of sulfur, However, too muchsulfur results in poor emciency in sulfur utilization per pass and favors the complete sulfurization of hydrocarbon material to carbon disulfide. 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. Generally speaking, best results are obtained using a weight ratio'of sulfur to hydrocarbon material varying between about 0.5 and about 4.0, although when butenes (or butadienes, when the process is operated to produce thlophene) Y constitute the bulk of the hydrocarbon material in the charge, the lower limit of the weight ratio maybe lower than 0.5.

EXAIVIPLEl Butene-l was processed with 10.9% by weight of sulfur at 1100 F. (exit gas temperature) in a coil reactor made of 0.15-inch inside diameter stainless steel tubing (coil volume 50 ccs.). Butene-i and liquid sulfur were pumped' through separate preheating coils for preheating to a temperature of about 1200 F. before mixing. The preheated vapors were combined through a simple Y-connectlon entering the reactor coil. The pressure drop across the reactor was 6 lbs. per

square inch, the average pressure being 3 pounds EXAMPLE 2 Butene-l was processed as in Example l with 29% by weight of sulfur. The reaction gases contained 26.6% by volume of hydrogen sulilde and the yield of butadiene per pass on butene-l charged was 18.1 by weight.

EXAMPLE 3 Butene-l was processed as in Example lvwith 36.0% by weight of sulfur. Tli'e reaction gases contained 33.8% by volume of `hydrogen suliide and theyield of butadiene per pass on butene-1 charged was 20.7% by weight.

61.6% by weight of sulfur.

contained 50.0% byvolume of hydrogen sulde and the yield of. butadiene per pass was 27.1% by'weight on the butene-l charged.

The selectivityof the reaction involved in ther.

process of the present invention depends primarily upon two variables, namely, the reaction f' temperature at which'the normal aliphatic hydrocarbon or hydrocarbons containing four carbon atoms per molecule are contacted with sulfur, and the vreaction time or the time during which contact. between `the reactants is mainltained atthe reaction temperature.

- 'j -The limits ofoperating temperature are xed bythe kinetics of the desired reaction andthe kinetics of possible side reactions.

l'found that the reaction temperature may vary We have between about 850 F. and about 1400 F. However,y when butanel is the' predominant hydrocarbon reactant in the charge,v the reaction temperature varies, preferably, between about 1100 F.'and about 1300 F.. when butadiene is the de sired'end-prodnct, and between aboutv 41000f1'.

andfabdutizooe F., when thiophene is the de sired-ehd-product. When butenes (or butajdienesl y'when lthiophene' is the desired end-product) vare the predominanthydrocarbon reactants in the V charge, .the reaction temperature varies, preferably;y .between about 900 F. and about 1300 F.,

whenbutadiene is the desired end-product, and n between about ,900?? and about 1100v F., when thiopheneis the desired end-product. Below the lower'. limit of the temperature range, as shown 4in Figures 2 and 3,'when the process is carried out kfor the purpose of producing thiophene, for ,"example, the reaction is so slow as to require a 4 large through-put of sulfur and a higher ratio of hydrocarbonrecycle for a xed amount of end-V product, therefore d'etracting from the economics of the operation.' Further, the secondary' reacltionof vtarlformation consumes a larger proportion of the charge. Above the upper limit of the temperature range, as shown in Figures 3 and 4,. when the process is operated to produce thiophene as the principal end-product, the secondary .reaction of degradation of hydrocarbon material in the charge takes precedence, thereby decreasing the yield `of Adesired product.

carbon disulfide. It must b e noted also, that at these high-temperatures, corrosion problems are 'at 'a maximum, corrosion increasing perceptibly with increasing temperature.

As expected,-we have found that the-,optimum` :reaction time depends upon 'the'.temperature, em-

p'loyed. Generally speaking, other variables re-A vmaining constant, the Alower `the temperaturqthe 4. "longer the reaction time. rThe reaction or contact time andthe reaction temperature are somewha-t fixed, onein relation to the other, bythe apparently being the Vrapidity with which heat can be supplied to the reaction mixture. The

vreaction is highly endothermic, requiring, ac-

cording to our experimental measurement, ap-

proximately 28,000 calories per 4gram molecular The reaction gases In addition,A tothis, high temperatures favor the formation of time is fixed, therefore, by the engineering problem of heat transfer V and by mechanical limita-- 5 tions,- such as allowable pressure drop across the reactor. Too long a reaction time at temperatures vin the neighborhood of the lower limit of the temperature rangeI results in loweroverall yields of thiophene or butadiene due to increased formation of heavy tar. On the other hand, too short a, reaction time atl temperatures in the neighborhoodv of the lower'limit of the temperature range, results in insumcient reaction. Accordingly, we have found that for best results, the time of reactionl is fixed by the reaction temperature. The relationship between reaction temperas ture and reactiontime is illustrated in the case where 'thiophene is the end-product, by the following tests:

It should be .noted that in these tests, as ythe reaction time. increasesand the temperature decreases, the yield per pass of thiophene is essentially constant. The lcalculated ultimate yield .of thiophene remains also substantially constant 4o being approximately 70% by weight based on the n-butane charged'. Likewise, the degree of degr'adationof the 'reactants and the yields of b y-productsremain substantially constant.. Test No. ''required the use of a reaction coil %inch iron-'pipe size, `and 52 feet in length. Accordingly, tests for vdetermining the possibility of employing longer periods of reaction time were notcarried outin view of the inconvenient lengths 0f alloy tubing which would be required for thereactor.l 1 At high temperatures, butane is more susceptible to cracking than butenes. Particularly A when the 'process is operated to produce butadiene as the end-product, and when normal butane is the hydrocarbon Ureactant, the temperature-time factor is more critical. Since, as y stated hereinbefore, it is undesirable for butane to be degraded to lower hydrocarbons such las methane, ethylene, propylene, etc.,`a temperature-time factor must be chosen which will give the least cracking and still allow a substantial dehydrogenation of the normal butane to butadiene. Fortunately, the dehydrogenation reaction with sulfur is much faster than the crack- .9 and 10. Consequently, by controlling. the reaction time at a given temperature, the cracking reaction can be kept at a very low level without 'markedly affecting the reaction with sulfur. By practically eliminating cracking through the use of very short reaction times, at a given temperature, the amount of useful recycle stock lis greatly increased and hence the selective conversion or theA ultimate yield is increased. v

vweight ofl thiophene produced from. normal butane. The lower limit of the range of reaction@ ing reaction. This` isv illustrated by Examples 8,

uid butanel (at 28 C.) and liquid sulfur (at 140- C.) were pumped through separate preheating coils for preheating to about 1200" F. before mixlng. 'Ihe preheated vapors were combined through a simple Y-connection entering the reactor coil.

The charge rates were 14.4 cc. of butane and 5.7 cc. of 'sulfur per minute. 'A partial vacuum was applied to the exit of the reactor coil to give an average pressure close to atmospheric. The reaction time was 0.10 second.

Quenching of the reaction mixture was accomplished by the stream of steam in the ejector which was used toprovduce the partial vacuum at the exit. The quenched gas was scrubbed iree of hydrogen sulfide (about 60% by volume) and collected in a gasometer for analysis. The recovery of gaseous product (free of HzS) -was 86% by weight of butane charged.

The analysis ofthe scrubbed gas was as follows:

Per cent by volume Methane Ethylene 7.6 Ethane 2.4 Propene 9.8 Propane 0.7 Butadiene 20.4 Butenes 15.7 Butane 32.6 Residue` 3.3

The yield of butadiene per pass was 19.0% by weight of butane, and the ycalculated ultimate conversion (including butene recycle) was 42%.

EXAMPLE9 n-Butane was processed with 77% by weight of sulfur at 14215 F. (exit gas temperature) in a stainless-steel baifled tube, constructed with the baflles extending out from the tube wall to provide heat conducting fins for better heat transfer to the rapidly flowing gas stream.. The volume of this reactor was 30 cc. Liquid butane (at 22 C.) and liquid sulfur (at 150 C.) were pumped through separate preheating coils and the preheated vapors combined at 1200 F. through a mixing jet consisting of two 11g-inch orifices opposing one another at a 180 angle.

The charge rates were 46.4 cc. of butane and 11.4 cc. of sulfur per minute. No vacuum was applied to the -reactor exit since' the pressure drop in this reactor was only 4 lbs. per square inch. The average pressure was 2 lbs. per square inch gauge and the reaction time lwas 0.026 second.

The recovery of HzS-free gas was 91.6% by weight of butane charge. The analysis of this gas was as follows:

- Y Per cent by volume Methane 0 Cn-hydrocarbons .2.6 Ca-hydrocarbons 2.9 Butadiene 13.8 Butenes 30.7 Butane 45.7 Residue 4.3

,weight oi butane charge, and

EXAMPLE 1o n-Butane was processed with 100% by weight of sulfur at 1210 F. in the same reactor described in Example 8. The pressure and reaction time were approximately the same as in the previous example.

The recovery of H2B-free gas was 88.6% by the analysis of this gas was 'as follows:

-Per cent by volume Methane 0.0 Cz-hydrocarbons 3.5 Ca-hydrocarbons 3.3 Butadiene 17.1 Butenes 17 6 Butane f 54.3 Residue 4.2

The yield of butadiene per pass was 14.5% by v weight of butane, and the calculatedf ultimate conversion (including butene recycle) was 47%.

We lhave found, for example, that in the conversion of butane to butadiene, the best temperature-time relationship is defined by a reaction time of 0.03-0.08 second at about 1200 F. or somewhat higher. Other tests were made in which the reaction with normal butane-for the conversion to butadiene was carried out at temperatures of 1000-1100" F. Only a relatively small conversionl to butadiene was noted (3-4% per pass). It would thus appear that, in so far as the conversion of `normal butane to butadiene is concerned, the preferred lower temperature limit for the process is around 1100 F. This is not, how-iv ever, the case with butenes, since tests indicate:

much better conversion was obtained at the higher temperatures within the temperatureA range of our process as indicated hereinbefore.

In view of the foregoing, the criteria to be used in determining optimum operating temperatures '.within the range 850-1400 F., and reaction times are to choose the degree of conversion 0fy product desired commensurate with operating costs such as heat input and'equipment costs, bearing in mind that within limits, the shorter the reaction time and concordantly, the higher the temperature, the larger lthe amount of desired endproduct which can be realized from a unit of given size per day.

In general, the relationship between perature o f reaction and reaction time is not singular with our invention. It is a well established and fairly well understood relationship in numerous reactions. In 4the present instance, wel

have found that butadiene or thiophene, as well as certain derivatives of thiophene, may be produced by reacting separately preheated sulfur and normal aliphatic hydrocarbons containing four carbon atoms per molecule at a temperature falling within the range varying between about 850 F. and about 1400" F., for a period of time selected to minimize the yields of secondary reaction prod- The yield of butadiene per passwas 12.04%.` by

weight of butane, and the calculated ultimate ucts, i. e., carbon disulde, hydrocarbons lower .than Cil-hydrocarbons, .and tar residueat the selected temperature. Accordingly, for the reaction temperature range o f ourv process,l i. e., 850 F. to 1400 F., when operating continuously with a reactor coil of suitable size and at a practical charge rate, we have found that the lowest practical limit of thetime of reaction isl the temof the order of 0.01 second at about 1400 F.' The upper practical limit of reaction time, other var iables remaining constant, will correspond to the lower limit of the temperature of reaction and may be of the order of several seconds. In view oi' the foregoing, it will'be appreciated that the period of time to be used at a selected reaction temperature within the range indicated, can be readily determined by one skilled in the art.

Separate preheating of .the hydrocarbon react- 'antandsulfun and quenching of the reaction mix- .ture are necessary for achieving thedesired control of the reaction time at a given reaction temperature. Indeed, our process is operative, as will be explained hereinafter, due to this feature of yseparate preheating of the reactants. is 'very important in the specific reaction producing butadiene or thio'phene. Without any inten'- tion of limiting Ithe scope of the present invention, it is suspected tha't a number of reactions occur in the reaction between the hydrocarbonA reactant and sulfur. In this connection, the following reactions should be noted: Cracking of the hydrocarbon reactantV destroying the four Ycarbon-atom straight-chain structure (four carbon ratoms in a straight chain being a prerequisite for the formation of butadiene or thiophene) dehydrogenation of the butane to the corresponding olenic and dioleflnic hydrocarbons; formation of tar high in sulfur; formation of carbon disulfide; and formation of thiophene. These reactions compete with one another. We have found .that the. rates of the crackingreaction and 'I'his of the formation of carbon disulfide are somewhat slower than that required for 4the formation of butadiene or thiophene. Accordingly, a proper control of the reaction time at a given reaction temperature achieved by separate preheating, mixing, heating at a given temperature for a corresponding period of time, and quenching, is necessary to produce high yields of thiophene or and fixed gases due tov a limited decomposition of the hydrocarbon reactant. Therate of the reaction producing tar is fairly close to that required for' the formation of butadiene and thiophene, and, therefore, the control of this reaction v is the favored reaction; and in the second place,

thesevheavy products are subsequently cracked in 'the reactor at the selected rea-ation temperature, causing undue coking. l Tests have shown that when .the reactants are heated .together up to temperatures Awithin the aforementioned reaction -temperature range, excessive tar forma.- tion always results. and in such quantities, that the reaction zone becomesv plugged with a heavy. carbonaceous deposit, in a very short period of time. Accordingly, it is essential in our process toseparately preheat each of the reactants, i. e., the hydrocarbon or the mixture of hydrocarbons constituting the hydrocarbon reactant, and sulfur, to such temperatures that when they are Abrought together, under proper conditions of ow. v

a temperature falling within the reaction temv peralture range is achieved, before effecting contact between them. In practice, this is effected ordinarily, by separately preheating each of the reactants to temperatures within the reaction i preheating and ultimate quenching of the reaction mixture, the yields of tar always approxi- Y mate those of thiophene or butadiene. However, certain valuable products, more particularly, certain thiopene derivatives, as pointed out in copending applications, Serial Number 721,453, filed January 10, 1947, and Serial No. 721,454, lled January 10, 1947, can be recovered from thetar. These thi'ophene derivatives are useful as intermediates in organic synthesis. This tar is a black,

mobile liquid which vanies slightly in composition f and physical properties, depending` upon there- -action conditions used in the process. sample had the followingl properties:

Heat and combustion 9084 B. t. u./lb.,

The tar was essentially miscible with a concen- .trated aqueous solutionof potassium hydroxide indicating the presence of constituents ofan butadiene with'limited yields of carbon disulde acidic nature. A sample of the tar was sub- .ected to vacuum distillation at 2 mm. absolute pressure and produced about-a 50% distillate, Aabout two-thirds of which uponredistillation boiled below C. at 2 mm. absolute pres-sure. Indications are that vacuum distillation is a destructive distillation sincey no product is steam distillable from the original tar, whereas the vacuum distillates can be steam distilled readily. The fraction boiling below 100 C. at 2 mm. absolute pressure was tested to obtain the following data:

TABLE II v Boiling Point, C. at 760 mm 171 l 166 Molecular Weight 128 116 Saponication No 438 483 Sulfur Content, Per Cent hiv) weight. 54. 9 55. 2 Carbon Content, Per Cent y weight.- 41. 9 41.3 Sulfur as SH. Per Cent hy weight (electrometric titration) f 28. 0. 27. 6 Sulfur Content of Mercury Salt, Per

Cent by weight 29. 6 29. 7 Refractive Index m20 l. 6153 Specific Gravity, 25/25 C 1.251 Solubility, Soluble in Aqueous KOH and Most 0rganic Solvents, such as Aromatic Hydrocarbons,

Ether, Chloroform, etc.

l Value reported in literature. Infrared spectrum analysis of this low-boiling vacuum distillate indicated the presence of the thiophene nucleus and SH group.

The fraction boiling (upon redistillation) at -135" C. at 2 mm. absolute pressure was again Iedistilled. A out boiling at 121123 C. at 2 A typical 13 absolute pressure was tested and the following data were obtained:

l Diicultly soluble in aqueous KOH.

The material does not undergo mercaptan reaction such as the formation of mercury salts, mercaptide formation with 2,4-dinitrochlorobenzene, etc.. and will not undergo mereaptan analysiselectrornetric method depending upon the precipitation of silver salt, indicating the absence oi SH groups.

As stated hereinbefore, for economical operation of the process, when thiophene is the desired end-product, we prefer not to use a hydrocarbon charge consisting predominantly of butadiene because of its tendency to polymerize in the preheater with consequent cracking and severe coking in the reactor. However, when butadiene is used in commotion with predominant amounts of butane and/or butenes, or suitable diluents which are inert with respect to sulfur and to other reaction products of the process, for example, nitrogen, carbon disulfide, carbon dioxide, etc., it canbe processed satisfactorily to give high' yields of thiophene. For eiective operation of our process, when thiophene is the desired end-product, we have found that butadienes should constitute a minor proportion (ordinarily, less than about 50% by weight) of the hydrocarbon feed.

In our process, the reaction is eiected, preferably, at atmospheric pressure or under suilicient pressure to cause the ow of the reactants through the reactor and auxiliary system, under the desired reaction conditions. Tests have shown that th'e yield per pass and ultimate yield of butadiene or thiophene decrease with increase in pressure. However, even at appreciable pressures, butadiene or 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 coil-type pipe reactor. With this type of reactor, the desired turbulent flow may be achieved with a pressure drop of about 1 to 20 pounds acrossthe coil, depending upon the size of the pipe and the length of the coil. Turbulent ilow promotes heat transfer and assures good mixing of th'e reacting vapors of sulfur and hydrocarbon material. l

In this connection, it should be noted that in so tar as the production of butadiene in accordance with the process of the present in'vention is concerned, it has beenl a rather unexpected result that good yields of butadiene are obtained without the use of diluents or without employing reduced pressures. when 'it is considered that all commercial processes for the production of butadiene use diluents page 30 (1942)] is carried out at a hereinbefore.

such as steam or other inert gases. or are carried out at greatly reduced pressures, of the order oi.' one-quarter oi an atmosphere .or below', absolute. For example, the recently described Houdry process [Oil and Gas Journal, 41, No, 15, l pressure of 5-10 inches of mercury, absolute. It is stated therein that the yield of butadiene per pass at atmospheric pressure is only about 2%, while at four inches or mercury, the yield isl about 12%- This appears to be characteristic of all previously described processes, and even the thermal conversion of naphthas and gas oils requires dilution of the reactants with 5-'10 volumes of steam, or other diluent, per volume of hydrocarbon vapor in order to obtain yields as high as" 5-8 per cent of butadiene.

The advantages of working at atmospheric pressure or without diluents are obvious. Thus, for a. given capacity plant operating under the conditions of the prior art, our process can convert up to eight times the amount of butane per unit time. Moreover, heat requirements are very substantially reduced by the elimination of diluents, and no special means are necessary to control the pressure as is the casein subatmospherio pressure installations.

Recycling of the unreacted portion of hydro-V carbon material in the eiuent stream hasbeen found to be a desirable scheme for increasing the ultimate yield of thiophene or butadiene. This has the same eiect as lengthening the reaction time without the attendant and undesirable degradation of hydrocarbon materialy referred to When butane is the hydrocarbon resctant and thiophene is the desired end-product, it is suspected that' the reaction proceeds stepwise with the formation of the corresponding olefinic hydrocarbon, diolenic hydrocarbon, and nally, thiop'hene, each step causing the formation, simultaneously, of hydrogen sulfide, molecular weight for molecular weight. These reactions occur con-currently and unreacted butane as well as butenes and butadienes are found in the effluent. Indeed, whether the process is operated for the production of butadiene or thiophene, butadiene and thiophene are always formed. Only traces of acetylenic hydrocarbons have been" found. These hydrocarbons in the efliuent (only butane and butenes, when the process is operated to produce butadiene) serve as recycle stream in the recycling operation. In this connection, and when the process is operated to produce thiophene, it must be observed that when butenes are the sole constituents of the hydrocarbon reactant, recycling of the hydrocarbons in the eiiiuent is not commercially feasible in view of the high concentration of butadienes in the recycle stock. However, and a's stated hereinbefore, butane or other suitable diluents may be added to the recycle stock and the latter proc- This is extremely important I essed to give high yields of thiophene.

Accordingly, a most important feature of our process is that it is flexible, it being possible'to produce butenes as well as butadienesv and thiophene from. butane, or butadienes and thiophene from butenes, or thiophene from butadiene.

A plant for practicing the process of our invention is illustrated diagrammatically in Figure 5. It is understood, of course, that certain mcdications 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 poc ess, with which this invention is concerned, are

clearly understood.

Referring now more particularly to Figure 5, which illustrates diagrammatically a plant for producing thiophene and/or butadiene, as Well as certain thiophene derivatives, asstated hereinbefore, in accordance with our process, normal butane 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 butane and sulfur are mixed at a point l prior to introduction into the reactor, and are then sent 300 F., by spraying' suitably with crude thiophene or some other liquid product of the process. The

quenched reaction products 'subsequently vare r passed into a tar-separator I0, wherein tar separates out and is sent iirst to a vacuum still 20 where mercaptothiophenes and other thiophene derivatives are recovered, and then to a sulfurrecovery plant I9. The reaction products free of the bulk of the tar, go to a filter II, to separate the tar mist. A Cottrell precipitato'r may be used as the mist collector if desired, The ltered 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 thiophene bottoms as the absorber liquid. The liquid bottoms from the condensate stripper column I2, go to a carbon disulfide tower I1 and the overhead to a compressor I3 and thence to a column I4` where Cs-hydrocarbon gases, gases lighter than Ca-hydrocarbons and hydrogen suliide are removed as overhead and sent to the sulfur-recovery plant I9. The bottoms from the column I4, consisting of Cil-hydrocarbons and materials having boiling points higher than C4- hydrocarbons; are passed into a column I5 where Cla-hydrocarbons are obtained as overhead and recirculated through a meter I 6 to the preheater 6, and thus returned to the process as recycle stock. (Valve 22 is opened while valves 2| and 23 are closed.) The bottoms from the column I5 are combined With the bottoms from the condensate stripper column I2, and sentv to the carbon 16 of about 0.05 second temperature to about 1200 F. v When the plant illustrated diagrammatically in Figure 5, is operated 'for-producing butadiene, as well as thiophene andthe thiophene derivatives. valves 2I and 23 are opened while valve 22 is closed. The overhead from the debutanizer I5 is passed into a butadiene absorber 24 Where the Cr-hydrocarbons vare contacted countercurrently with a selective butadiene absorbent, suitably, an ammoniacal cuprous chloride aqueous solution.

. The butane and butenes are obtained as overhead :and are circulated through the meter I6 to the preheater 5, and Athus returned to the process as recycle stock. butadiene is pumped by a pump 25 to a butadiene stripper column 26 where butadiene is removed from the absorbent with heat, butadiene comes oil the stripper column 26 as overhead and is sent to storage. The hot absorbent free of butadiene is pumped by a pump 21 through a cooler 28 back to the butadiene absorber 24.

Detailed examples illustrating modes of producing butadiene in accordance with our invention have already been given hereinbefore.

The following detailed examples are for the I purpose of illustrating modes of producing thiophene in accordance withour invention, it being clearing understood that the invention is not to be considered aslimited to the specific manipulations and conditions set forth hereinafter.

EXAMPLE 1 A mixture containing 30% by volume of 1,3-

butadiene and '70% by volume of normal butane was charged into a preheater at the rateof 35 grams per minute and heated to a temperature of 1100 F. Sulfur was` charged to a separate preheater at a rate of 28 grams per minute and heated to a temperature of 1100 F. The two streams were sent through a mixing nozzle and thence through a. baffled tube reactor of 50 c. c.

/volume constructed of 27% vchromium stainless y steel maintained at a temperature Vof 1300 F.

The reaction product was quenchedvwith a Water spray, passed through a small Cottrell precipitator to remove tar mist, and scrubbed through a Liquid kproduct was condensed and separated in a Water cooler and ice trap and the residual gas metered. 49% of the hydrocarbon material charged Went to liquid product and tar. Fractionation of apordisulfide tower I1.` Carbon disulfide is taken oil" as overhead from the tower I'I and sent to storage, While the bottoms from the tower I1 are densate stripper column I2 and/ or as a quenching,4

medium.

In a typical operation, the hydrocarbon material charged to the preheater coil 6 is made upof a normal butane cut containing varying amounts of butenes, obtained from a cracking unit for the conversion of gas oil into gasoline.

Sulfur is charged to the preheater 3, -in amounts tion of the stablized (i.v e., after removal of C4-hydrocarbons and lighter constituents) liquid showedthe followingcomposition:

- I Per cent Carbon disulfide 9.0 Thiophene Y v 80.5 Residue (mostly thiophene) 10.5

EXAMPLE 2 4959 grams of technical butene-Z (0.9% isobutylene, 98.5% butene-Z and 0.6% normal butane, `by Podbielniak distillation), were charged at the rate of 49 grams per minute to a preheater l coil consisting of 20 feet of 0.15 inch internal diameter, 18-8 stainless .steel tubing, immersed in a lead bath, kept at 1190"- F., and preheated to a temperature of 1160" F. 17230 grams of molten sulfur were charged at the rate of 71.7 grams per minute to a preheater coil consisting of 20 feet of 1g-inch iron pipe size, 27% chromium stainless to produce a mixture at .'I having a Weight .ratio of sulfur vto butane cut. of about 1.0 and the charge rates are adjusted t0 sivea reaction ktime steel.. tubing, immersed in a lead bath kept at a temperature of 1320, F., and preheated to a temperature of 1290F. The preheated reactants The absorbent containing the 'were then sent through a mixing nozzle and then through a reactor consisting of 12 feet of 1/-inch iron pipe size, 27% chromium stainless steel tubing immersed in a lead bath kept at a temperature of 1260 F., to give a temperature at the entrance to the quench tower, of 1250 F. The pressure drop across the reactor was 12 pounds per square inch gauge, and the reaction time was 0.03 second. The reaction product was quenched with a water spray, sent through water-cooled heat exchangers to a tar trap, and thence to a glasswool filter where the tar mist was filtered out. The filtered gas was subsequently sent. through a countercurrent caustic scrubber maintained at a temperature of 176 F. for the removal of hydrogen sulfide. The remaining reaction product stream was sent through an efficient cooling system and finally to an ice trap for collecting the crude thiophene. The off-gases from the ice trap were metered and subjected to Podbielniak distillation with the following results:

. Mole per cent Hydrogen sulfide 0.4 3.4

-Methane Cz-hydrocarbons 2.7 Cs-hydrocarbons 6.3 Butenes 49.6 -Butadiene 35.2 Butane I 1.0 Residue 'l 1.4

The following products were obtained:

. Grams Hydrogen sulflde 3,892 Liquid product 3,340 Oft-gases 1,610 Tar 3,020

The liquid product was fractionated onl a 15- plate'column with the following results:

Per'cent by lweight C4-hydrocarbons 17.1 Carbon disulfide 8.9 Thiophene 71.5 Residue 2.5

EXAMPLE 3 v tained in the ice trap of Example 2; the compresses gases passing through a water-cooled heat-exchanger and thence, to a liquid hydrocarbon reservoir. The pressure in the lhydrocarbon reservoir was maintained at 80 pounds per square inch gauge by bleeding off the proper amount of light gases resulting from thermal cracking. The recycle stream sent to the hydrocarbon preheater had the following composition:

Mole per cent Hydrogen sulde Methane 1.0 (l2-hydrocarbons 4.2 Cs-hydrocarbons 8.0 Butenes y 14.2 Butadiene 23.3 Butane 47.2 Residue 1.0

18 i In this run, 9860 grams of sulfur were charged to the sulfur preheater ata rate of 64.4 grams per minute. The pressure drop across the reactor Was 8 pounds per square inch gauge. and the reaction time was 0.04 second.

The following results were obtained:

Light gases 1,073 i Mole per cent Hydrogen sulfide 1.0 Methane 36.6 Cz-hydrocarbons 16.1 Ca-hydrocarbons 5.0 Butadiene 13.0 Butenes 12.2 Butane 15.6 Residue 0.6 Hydrogen sulfide '7,320 Tar 2,645

Ultimate analysis:

Per cent by weight Carbon 25.2 Hydrogen 1.8 Sulfur 73.0 Crude thiophene 3,456

Per cent by Weight Ct-hydrocarbons 15.4 Carbon disulfide 10.2 Thiophene 72.4 Bottoms 2.0

This application is a continuation-in-part of copending application Serial Number 490,868, filed June 15, 1943, now abandoned.

The present. invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it is therefore desired that the present embodiments Vbe considered in all respects as illustrative and not restrictive, reference being had to the appended claims rather than to the foregoing description to indicate the scope of the invention.

We claim:

1. The process for producingv valuable organic compounds from normal C4hydrocarbons,.which comprises vseparately preheating sulfur and a C4-hydrocarbon selected from the group consisting of normal butane,:normal butenes, and butadienes, to temperatures such that combining said sulfur and said hydrocarbon will give a reaction mixture having a temperature varying between 850 F. and about 1400 F.; mixing the preheated sulfur and the preheated hydrocarbon; reacting said preheated sulfur with said preheated hydrocarbon lat a reaction temperature varyingbetween about 850 F. and about 1400c F. to yield a mixture containing said organic cornpounds; andimmediately reducing the temperature of the mixture containing said organic compounds to a temperature of less than 850 F.

2. The process for producing butadiene, which comprises separately preheating sulfur and normal butane, to temperatures such that combining said sulfur and said normal'butane will give a reaction mixture having a'temperature varying between about 850 F. and about 1400 F.; mixing the preheated sulfur and the preheated normal butane; reacting said preheated sulfurwith said preheated normal butane at a reactiontemperature varying between 850 F. and about 1400 F. for a period of time 'selected to minimize the yields of hydrocarbons containing llesstluanfour carbon atoms per molecule and carbon disulfide at said reaction temperature, toyield a butadiene-containing mixture; immediately reducing Grams' the temperature of the butadiene-containing mixture to a temperature orf less than 850 F.; and separating the butadiene from said butadienecontaining mixture.

3. 'I'he process for producting butadiene, which comprises separately preheating sulfur and normal butane, to temperatures such that combining said sulfur and said normal butane will give a reactionmixture having a temperature varying between vabout 1100 F. and about 1300 F.; mixing the preheated sulfur and the preheated normal butane; reacting said preheated sulfur with said preheated normal butane at a reaction temperature varying between about 1100 F. and about 1300 F. for a period 'of time selected to minimize the yields c-f hydrocarbons containing less than four carbon atoms per molecule'and carbon disulde at said reaction temperature, to yield a butadiene-containing mixture; immediately reducing the temperature of the butadienecontaining mixture to a temperature of less than 'about 850 F.; and separating the butadiene from said butadiene-containing mixture.

4. 'Ihe process for producing butadiene, which vcomprises separately preheating sulfur .and a normal butene, to temperatures such that. combining said sulfur and saidnormal butene will give a reaction mixture having a temperature varying between about 850 F. and about 1400 F.; mixing the-preheated sulfur and the preheated normal butene; reacting said preheated sulfur with said preheated normal butene at a f reaction temperature varying between 850 F. and about 1400" F. for a period of time selected to minimizethe yields of hydrocarbons containi ing less than four carbon atoms per molecule and carbon disulfide at said reaction temperature, to yield a butadiene-containing mixture;

n immediately reducing the temperature of the butadiene-containing mixture to a temperature yof less than.850 F.; and separating the butadienefrom said butadiene-containing mixture. The process for producing butadiene,'which comprises separately preheating sulfur and a normal butene, to temperatures such that combining said sulfur and said normal butene will give a reaction .mixture having a temperature varying between about 900 F. and about 1300 F.; mixing the preheated sulfur and the preheat- 1 ed normal butene; reacting said preheated sulfur with said preheated normal butenev at a reaction temperature varying between about 900 F. and about 1300 F. for a period of time selected to minimize the yields of' hydrocarbons contain- `ing lessA than four carbon atoms per molecule and carbon disulfide at said reaction temperature. to yield a butadiene-containing mixture; immediately reducing .the temperature of the butadiene-containing mixture to a temperature 1 of less than about 850 F.; and separating the butadiene from -said butadiene-containing mixture.

6. The process for producing thiophene, which comprises separately preheating sulfur and normal butane, the temperatures such thatcombiningsaid sulfur and said normal butene will give a reaction mixture having a temperature varying between about 850 F. and about 1400 F.; mixing the preheated sulfur -and the preheated normal butane; reacting said preheated sulfur with-said preheated normal butane at a reaction temperature varying between 850 F. and about 1400 F. for a period of timel selected to minimize the yields of hydrocarbons containing less than four carbon atoms perl molecule ing the preheated sulfur and the preheated normal butane; reacting said preheated sulfur with said preheated normal butane at a reaction temperature varying between about 1000 F. and about 1200 F. for a period of time selected to minimize the yields of hydrocarbons containing vless than four carbon atoms per molecule and carbon disulfide at said reaction temperature, to yield a thiophene-containing mixture; immediately reducing the temperature of the thiophene-containing mixture to a temperature of less than about 850 F.; and separating the thiophene from said thiophene-containing mixture.,A

8. The process for producing thiophene, which comprises separately preheating sulfur and a normal butene, to temperatures such that combining said sulfur and said normalbuten'e will give a reaction mixture having a temperature varying between about 850 F. and about 1400 F.; mixing the preheated sulfur and the preheated normal butene; reacting said preheated sulfur with said preheated normal butene at a reaction temperature varying between 850 F. and about 1400 F. for a peroid 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 thiophene-containing mixture; immediately reducing the temperature of the thiophene-containing mixture to a temperature of less than 850 F.; and separating the thiophene from said thiophene-containing mixture.

9. The process for producing thiophene, which comprisesseparately preheating sulfur and a normal butene, to temperatures such that combining said sulfur and said normal butene will give a reaction mixture having atemperature varying between about 4900 F. and about 1100 F.; mixing the preheated sulfur and the preheated normal butene; reacting said preheated sulfur with said preheated normalbutene at a reaction temperature varying between about 900 F. and about 11005 F. for a period of time selected to minimize the yields of hydrocarbons lcontain-V ing less than four carbon atoms per molecule and carbon disulfide at said reaction temperature, to yield a thiophene-containing mixture; Y

immediately reducing the temperature of the thiophene-containing mixture to a temperature of less than about 850 F.; and separating the thiophene from said thiophene-containing mixturc.- s

10. The process for producing thiophene, which comprises separately preheating sulfur and a hydrocarbon feed comprising minor proportions of` a butadiene, totemperatures such that combining said sulfur and said hydrocarbon feed will give a reaction mixture having a temperature varying -between about 850 F. and about l400 F.; mixing thel preheated sulfur and the preheated hydrocarbon feed; reacting said preheated sulfur with said preheated hydrocarbon feed at a reactionA temperature varying between 850 F. and

about 1400 F. for a period of time selected to mlnimize the yields of hydrocarbons containing less than four carbon atoms per molecule and carbon disulfide at said reaction temperature, to yield a thiophene-containing mixture; immediately reducing the temperature of the thiophene-containing mixture to a temperature of less than 850 F.; and separating the thiophene from said thiophene-containing mixture.

11. The process for producing thlophene, which comprises separately preheating sulfur and a hydrocarbon feed comprising minor proportions oi.' a butadiene, to temperatures such that combining said sulfur and said hydrocarbon feed will give a reaction mixture having a temperature varying between about 900 F. and about 1100 F.; mixing the preheated sulfur and the preheated hyrocarbon feed; reacting said preheated sulfur with said preheated hydrocarbon feed at a reaction temperature varying between about 900" F. and about 1100 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 thiophene-containing mixture; immediately reducing the temperature of the thiophenecontaining mixture to a temperature of less than about 850 F.; and separating the thiophene vfrom said thiophene-containing mixture.

12. The tar obtained by the process which comprises separately preheating sulfur and a C4-hydrocarbon selected from the groupconsisting of normal butane, normal butenes, and butadienes, to temperatures such that combining said sulfur and said hydrocarbon will give a reaction mixture having a temperature varying between about 850 F. and about lA0O F.; mixing the preheated sulfur and the preheated hydrocarbon; reacting said preheated sulfur with said preheated hydrocarbon at a reaction temperature varying between 850 F. and about 1400 F. t0 yield a mixture containing said tar; immediately reducing the temperature of the mixture containing said tar to a temperature of less than 850 F.; and separating the tar from said mixture.

four carbon atoms per molecule and carbon disulde at said reaction temperature, to yield a mixture containing said tar'; immediately reducing the temperature of the mixture containing said tar to a temperature of less than about 850 F.; and separating the tar from said mixture.

14. The tar obtained by the process which comatoms per molecule and carbon disulde at said reaction temperature, to yield a mixture containing said tar; immediately reducing the temperature of the mixture containing said tar to a temperature of less than about 850 F.; and separating the tar from said mixture.

15. vThe tar obtained by the process which comprises separately preheating sulfur and a hydrocarbon feed comprising minor proportions of a 13. The tar obtained by the process which comprises separately preheating sulfur and normal butane, to temperatures such that combining said sulfur and said normal butane will give a reaction mixture having a temperature varying between about 1000 F. and about 1200 F.; mixing the preheated sulfur and the preheated normal butane; reacting said preheated sulfur with said preheated normal butane at a reaction temperature varying between about 1000 F. and about l200 F. for a period of time selected to minimize the yields of hydrocarbons containing less than butadiene,v to temperatures such that combining said sulfur and said hydrocarbon feed will give a reaction mixture having a temperature varying between about 900 F. and about 1100 F.; mixingv the preheated sulfur and the preheated hydrocarbon feed; reacting said preheated sulfur with said preheated hydrocarbon feed at a reaction temperature varying between about 900 F. and

about 1100 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 mixture containing said tar; vimmediately reducing the temperature of the mixture containing said tar to a temperature of less than about 850 F.; and separating the tar from said mixture.

ROWLAND C. HAN SFORD. HERBERT E. RASMUSSEN. ALEXANDER N. SACHANEN. l

REFERENCES CITED The following references are o1 record inthe file of this patent:

UNITED STATES PATENTS Certicate o1' Correction A Patent No. 2,450,659. October 5, 1948.

ROWLAND C. HANSFORD ET AL.

It isherehy certified that errors appear in the printed specification of the ahove numbered patent requiring correction as follows.:

Column', line 56, for quenc-ed read quenched; column 12, line 34, for the 'I Words Heat and combustion read Heat of combustion; column 16, line 29, for clearg read clearly; column 17, line 58, for presses read pressed; column 19, line .5, claim 3, for producting read producing;

`and that the seid Letters Patent should be read with these corrections therein thatl the seme may conform to the record of they case in the Patent Oice.

Signed and sealed this 24th day of May,A. D. 1949.

THOMAS F. MURPHY,

Am'stantOommzsaz'oner of Patente. l

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