US2409815A - Manufacture of olefins - Google Patents

Description

C. K. VILAND EI'AL v MANUFACTURE OF OLEFINS Filed Jan. 25, 1943 INI/M7025 Cmef /fe/wvfr/-l V/LA/vo HfescHaL Y. HYDE Patented Oct. 22, 1946 MANUFACTURE OF OLEFINS Clare Kenneth Viland, Martinez, and Herschel Y.

Hyde, Associated, Calif., assignors to Tide Water Associated Oil Company, San Francisco, Calif., a corporation of Delaware Application January 25, 1943, Serial No. 473,456

`8 Claims. (Cl. 260-683) This invention relates to the manufacture of olefnic feed stock for alkylation and similar processes Where a high concentration of olens is desirable and has for a principal object the manufacturer of C4 and C5 fractions containing unusually high percentages of olenic hydrocarbons.

Another object of the invention is to provide materials peculiarly adapted for pyrolytic conversion into desired olens.

A further object is to reduce the quantity of normal pentane commonly present in stocks charged to alkylation or similar processes thereby increasing the plant capacity by elimination of a large proportion of those hydrocarbons not entering into the reaction.

Other objects will be apparent from the following description.

In the manufacture of modern aviation gasoline the alkylation process has become one of the most commonly used methods of obtaining gasoline fractions of high antiknock rating. As is well known, this process as most generally practiced comprises the formation of branch-chain paraffins chiefly in the boiling range of the octanes by the chemical combinati-on of isobutane with butylenes. However, especially in cases where the supply ofbutylenes is inadequate to meet the demands for aviation gasoline, the alkylation process is also used to produce good antiknock gasoline components by reacting isobutane with amylenes.

The quantity of alkylate which may be produced in any given area, therefore, is limited by the available supply of isobutane, butylenes and amylenes as well as by the capacity of the alkylation plants. Present demands for aviation gasoline have resulted in the constunption of practically the entire supply of naturally occurring isobutane and numerous renners have undertaken the installation of isomerization processes to augment the supply thereof. The chief source, if not the entire supply, of the required butylenes and amylenes is from the by-products of various pyrolytic processes, such as cracking and polymerization, which are primarily designed for the manufacture of hydrocarbons within the gasoline boiling range. Due to modern demands for butylenes and amylenes for alkylation purposes numerous pyrolytic plants are being operated principally for their production of these olefins.

As commonly practiced, butylenes for the alkylation process are obtained by isolating a C4 cut from the products of the pyrolytic cracking and/ or polymerization processes. Ordinarily this C4 cut will contain from about to 45% of butylenes,

2 the remainder being chiefly normal butane. As the normal butane cannot be readily` fractionated from the butylenes without the use of extensive Y fractionating equipment, it is common practice to charge the entire C4 cut to the alkylation process, along with the required amounts of isobutane.

As the normal butane does not enter into the alkylation reaction, it passes through the plant unchanged and is fractionated from the products of the reaction. This procedure offers difficulties, however, when normal butane is present in large amounts. First, the throughput capacity of the alkylation reactor is reduced in proportion to the amount of the inert normal butane which is present. Second, in order to separate the normal butane from the products, a heavy load is placed on the fractionating equipment of the alkylation plant. Third, since the alkylation process requires the recirculation of large amounts of iso- Vbutane for the proper functioning of the process,

the separation therefrom of the inert normal butane Valways results in the loss of substantial quantities of valuable isobutane into Ythe normal butane due to imperfect fractionation. From the above it is seen that it is desirable to charge to the alkylation process a C4 cut with as 10W a content of normal butane as possible.

Likewise, when amylenes are alkylated, the amylenes are obtained by isolatingV a C5 cut from the products of the pyrolytic cracking and/or polymerization processes. Ordinarily this C5 cut will contain from about 40% to 50% of amylenes, the remainder being chiefly pentanes. As the pentanes cannot be readily fractionated from the amylenes without the use of extensive fractionating equipment, it is common practice to charge the entire. C5 cut to the alkylation process, along with the required amounts of isobutane. As the normal pentane does not enter into the alkylation reaction, it passes through the plant unchanged and is fractionated from the products of the reaction. The presence of large amounts of the norma1 pentane offers diiculties similar to the presence of normal butane during butylene alkylation.`

The present invention provides a method for producing larger amounts of amylenes from pyrolytic processes than are normally obtained therefrom, and provides a C5 fraction containing from about to 80% amylenes. In this way not only is the available supply of amylenes increased, but also a C5 cut is provided which con# tainsasubstantially lower percentage of unreactive normal pentane. Simultaneously there is produced a C4 cut which contains from about 40% to 60% butylenes, which provides a more efficient C4 fraction for butylene alkylation than is normally obtained from pyrolytic processes. The overall effect, therefore, is to furnish additional quantities of butylenes and amylenes and, coincidentally, tov increase the capacities of the alkylation plants, whether alkylating amylenes or butylenes.

Briefly described, the invention comprises subjecting normal hexane to pyrolytic decomposition in the presence of substantial amounts iA Dropylene and ethylene. When normal hexane is subjected to temperatures in the range, of 100,0`ov

to 1300 F., it is decomposed'into various ole- In accordance with the invention substantial n ,25.

quantities of propylene and ethylene are mixed with the normal hexaneY prior to Carr-ying out the decomposition, The presence of the -Cz and especially the C3 olens tends to suppress. (2) and (il). and thereby increases the'amount of material undergoingV reactions 1 and 3, resulting` inthe formation ofy larger amounts ofamylenes and butylenes. Reaction 4 may be still further retarded by the addition of propane also Vto the mixture prior to pyrolys'is. Likewise, if desired, ethane may` also, be added resulting in a suppression of Reaction 3 with a correspondingdecrease in theA production of'but-ylenes andan increase in amylene production.

From the above :it may be seen' thatjvvhen nor. malA hexane issubjected to pyrolysis toproduce amylenes, the percentage of amylenes producedmaybe increased by increasing the concentration ofan'y one of" the Czior C3 hydrocarbons present during the reaction. However, best results are obtained by increasing the concentration of alll the C2 and C3 hydrocarbons, especially thelC'z and C3V olens.

Under the temperature conditions ofthe reaction, andl especially in the temperature rangen-i 1050 F. to 115,0" E.; 'there occur, 'simultaneouslywithl the decomposition ofithehexane, 'polymerizing'reactions among the C2 andCa 'hydrocarbons' present resulting in the formation of additional" quantities of amylenes and butylenes `together with a large quantity of polymer' gasoline of good anti-knock value. Isobutane, normalbu-tane, isopentane, normal pentane, and, in minor proportions, polymer tarsl and other products are also formed. As stated above, the isobutane is-avaluable constituent'for the feed stock to the alkyl-a;- tion plant Similarly,l isopentane is useful4 as a feed stock for alkylation.

ratio. of about 7.11. In the C2 and C3 hydrocarbons charged as above, a ratio of 20% C2 and 80% C3 hydrocarbons has been fund to give good results.

In carrying out the process of the invention it may be convenient to use a conventional thermal polymerization plant. The accompanying drawing shows diagramniatically a typical thermal polymerization plant with modications for carrying out lthe invention. In accordance with the invention normal hexane in line I and C2 and Cs hydrocarbons in line 2 are charged to pyrolytic Zone @through line 5; the proportion of each being controlled by valves 3 and il. In pyrolytic zone the mixture isheated to the reaction temperature in coils? and 8 and the resulting products. leave, through line 9. Suitable pressure is maintained upon the mixture in the pyrolytic zone by meansof valve Iii. From line 9 the products enter fractionating Zone I l (which may advantageously comprise several, fractionating columns arranged in accordance with well known principles of fractional distillation) wherein they.. are fractionally distilled'. to recover desired.; fractions, shown diagrammatically as leaving through lines I2, I3; I Il, I5, IBI, and. Ia'I' in the respective order. of their boilingranges.` Through line I2 is with drawn methane, and any hydrogen, formed; during the reaction and suilicient ethylene (and ethane, if desired) tov maintain the concentration of C2 hydrocarbons Withdrawn through line I3 within the desiredy range. This.y overhead gaseous fraction mayI be used as fuel. The remain.- ing C2 hydrocarbons togetherf'with the C3 hydro. carbons are withdrawn through line Ifi and re.- cycled to the process throughv lines` t8. and. Ii.9 being mixed with incoming fresh. charge of: ,C2 and C3. hydrocarbons in line f2 or 5.' Through line I4 is withdrawn a C4 cut which, under. the.

operating conditions. of the' invention, wilifcontain from about 40%4 tot 60% of butylenes.A 40- cut which, underv the operating conditions ofithe invention, Will. contain l'rom about 601% to..30.%`

of amylenes. As previously. stated, these. Grandi C5 cuts may advantageously be usedlas. ole'nicI feed. for alkylation processes. 'Through line,x I'di is withdrawn a depentanized polymer gasoline; While. poly-mer tars leave the fractionating Zone through lineA Irl". If` desired;normalhexanamay` be fractionated from the polymer gasoline in la'. second fractionati-ngY zone (notshown)Y andoree cycled to the process (through lines not shown)A to be..mixed with thefresh normal hexanein; line I or 5.

Normal hexane: for` lconductingrthe` process off.

the invention maybeproducedlin :most reneries.:A manufacturing aviation gasoline, being. obtainec` as a Icy-product of relatively.. lowv value in.-the.- fractionation. ci?A straight rungasoline stocksgandf. other stocks, for the production. 'of' i'soehexane. used as aningredient in.. aviationgasoline; .'zAsLl is weilfknown, the normalhexane thus obtained;

is generally notof 100%. purity.. According to. common practice `such a normal hexane fraction.

on the eiiiciencyv of the fractionation, a.' small amount of hydrocarbons-having higher lor flower boiling points mayalsof'be present', but generallyl not in excess of 5%.-

While, foroverall reiineryemciency, it: is desire i able to separatenormal hexane oi-1as-highpurity as possible, the process of the invention is ada-pt@ edV to operate satisfactorily on normal hexane Through line I5 is withdrawn. the desired Cs.

between i45 F; and 1605 F., suchas-f forA exa'1n-..`

stocks within the abovel range of purity. In the appended claims this range of purity is intended to come Within the scope of the term consisting essentially of normal hexane.

4Following is an example of the process of the invention conducted in a conventional thermal polymerization plant. A freshcharge consisting of 600 barrels per day of propylene, 200 barrels per day of propane, and 1,000 barrels per day` of normal hexane stock, together with 4,000 barrels per day of recycled C3 hydrocarbons and 1,000 barrels per dayl of recycled C2 hydrocarbons, was charged to the heating coil of the polymerizae tion plant wherein the temperature was raised to 1125 F. The products from the heating coil were passed to the reaction section wherein the temperature was reduced to 1050 F. over a period of about 12 minutes. The products were then fractionally distilled into a gas fraction, a recycle fraction consisting of all the Cs hydrocarbons together with a portion of the Cz hydrocarbons formed, a C4 cutcontaining all theCr hydrocar` bons formed, a C5 cut containing all the C5 hy drocarbons formed, a depentanized polymer gasoline fraction, and a residual tar fraction. It was found that the C4 fraction contained 50% of oleflns andthe C5 fraction contained 65% of olefins. The followingtable shows results obtained compared to conventional operations where Ca hydrocarbons are polymerized under similar operating conditions. Y

Conventionaleg allthernial po ymerizato mventlon tion Fresh charge, bbL/day:

Propylene 600 600 Propane 200 N. hexane stock (l45-l60 F. 1, 000

Total l, 800 800 Recycle stock, bbl/day:

C2 hydrocarbons l, 000 1, 000 O3 hydrocarbons 4, 000 4, 000

25 125 50 95 48 2 150 50 N-pcntanc. 40 30 Other products l, 320 585 'IotafL lt 1,800 S00 Analysis o 4 frac ion per cen.:

1s0butane. 12. o 21. 7 Buty1enes 50. 0 23. 5 Nbutanc 38. 0 a4. 8

TotaLC. 1.; 100. 0 100.0 Analysis of 5 fraction per cen z Isopentane I 17. 4 2G. 0 Amylenes 65. 2 50. 0 N-pentane 17. 4 30. 0

Total 100. 0 100. 0

From the above table it is seen that, by introducing normal hexane into the charging Istock of the polymerization plant in accordance with the invention, the yield of C4 and C5 hydrocarbons is greatly increased together with a substantial overall gain in the percentage of olens therein.

Although a conventional thermal alkylation plant using normal operating conditions of time, temperature, and pressure is well adapted to the carrying out of the invention and although such operation is a preferred form of the invention, the invention in a broader sense is not limited to such operation. Any equipment may be used which is capable of maintaining the mixture of normal hexane and C2 and Cs hydrocarbons at ay cracking temperature for suilicient time that the desired amount oftolens is formed and various apparatus may suggest themselves to a skilled engineer. i

`Conventional polymerization furnaces are generally divided into two sections; the tubes'i or coils cf the `iirst sectionbeingsubjected to a higher degree of heat than those of the second section..

The process of the inventionmaybe carried out in a single coil subjectedto the necessary temperature, or a combination of heating coil\and reaction chamber `may be used if so desired.

Pressures employed in conventional polymerization plants are usually in the order of 300Y to 500 lbs. per squarench'at the outlet transfer line. While this pressure is preferable, for operating reasons, in the practice of the invention, other Likewise, the'charge to the conventional polymerization plant (including both the feed and recycle stocks) is generally in the liquid phase.

This is, however, merely an expedient and the charge of normal hexane and C2 and C3 hydro` carbons according to the invention may be either in the liquid or vapor phase as desired. Obviously, at the cracking temperatures involved, the materials undergoing the reactions will be above the critical temperature, and consequently, in the vapor phase.

We claim:

1. The process of producing a mixture of C5 hydrocarbons containing a high proportion of amylenes which comprises: subjecting a hydrocarbon fraction consisting essentially of normal hexane to a temperature in the range of 1000 F. to 1300 F. while in the presence of added amounts of hydrocarbons from the group consisting of ethane, ethylene, propane, and propylene and in the substantial absence of other added hydrocarbons; fractionally distilling the resulting products; and separating therefrom a mixture of C5 hydrocarbons; the molal ratio of normal hexane to Cz and C3 hydrocarbons subjected to the reaction being between about 1:1 and about 1:7.

2. The process according to claim 1 wherein the molal ratio of normal hexane to C2 and C3 hydrocarbons subjected to the reaction is not greater than 1:3.

3. The process according to claim l wherein the molal ratio of normal hexane to Cz and C3 hydrocarbons subjected to the reaction is about 1:7.

4. The process of producing a mixture of C5 hydrocarbons containing a high proportion of amylenes, which comprises: subjecting a hydrocarbon fraction consisting essentially of normal hexane to a temperature in the range of about 1050 F. to about 1150 F. while in the presence of added amounts of hydrocarbons from the group consisting of ethane, ethylene, propane. and propylene and in the substantial absence of other added hydrocarbons; fractionally distillingV the resulting products; and separating therefrom a mixture of C5 hydrocarbons; the molal ratio of normal hexane to Cz and C3 hydrocarbons subacoge-1s.

comprises-1 subjecting a `l'iydrocarbon :Eraction` consisting essentially-of normal hexane to atem,

perature in the. range` of 1000o F'. to 1300" F. while;

in the presence-of added amounts of hydrocarbons from` they group consisting of ethylene; propane, and propylene and inthe substantial ab-r sence of other. added hydrocarbons; fraotionally distilling. the resulting products; and separating therefrom a mixture of C hydrocarbons and a mixture. ofV C4 hydrocarbons; the molal ratio of normal hexane to C2 and C3 hydrocarbons subjected to the reactionV being between about 1:1 and about 1:7.

6. The process of producing, a mixture of C5l lxydrocarbons` containing a high proportion of amylenes which comprises: flowing.. ay stream of hydrocarbons. consisting essentially of normal. hexane through a conduit', simultaneously owing a stream consistingv of hydrocarbons lighter than C4 hydrocarbons. and heavier than methane through said conduit in adrnixture. with-said normal hexane while in the substantial absence of other added hydrocarbons, heating the mixture in conduit to. a temperature. between 1000" F; and 1300" F., maintaining, the mixture at said' temperature. for. sucient time thatl a. portion ofthe normal hexanefs.y cracked. forming. amylenesp, iid@ ducingthe. temperature'of the. resulting products, fractionally1 distilling the resulting products and separating therefrom a, fraction composed'ma-in-ly of the C5; hydrocarbons present in said products; the molal rati'o of' normal hexane to C2V and C3 hydrocarbons subjected. to the. reaction being;v betweenabout 11: 1: and about. 1:7.V

7. A method comprising thermally cracking at..

a. temperature in the-orderof v1000" F. to 1300o l?. a. mixture of. normal hexane, Cahydrocarbonsand Cs; hydrocarbons while in the. substantial absence of other added hydrocarbons and fractiona'lly distilling a. Ceiraction from'the resulting: products;

the rnolal` ratio: of normal hexane to C2 and C3;V

hydrocarbons subjected tothe reaction being between about. 1: 1 and about 1 8. A processY of' producingl C51 hydrocarbonsl which comprises: heating' normal hexaneto aA crackingtempera'ture in the order of. 10009 F.` to 1300? while inthe presence of an added quantity of Czfand Cs hydrocarbons and in the sub.-v stantial absence ofl other added hydrocarbons, and maintaining such temperatureV for a period of time sufficient to form a C5 fractionr containing in: the order of from 6,0%, to of olei'his;` the molaliratio of* normal hexane-toCz and Cshydrocarbons. subjected to the reaction beingV between about 11:1 and. about 1:7.

CLARE KENNETH' VILAlND. HERsCI-IEL Y. HYDE.

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