US2396753A - Polymerization of hydrocarbons - Google Patents

Description

March 19, R. RGSEN ET AL POLYMERIZATION OF HYDROCARBONS Filed oct. 1, 1940 gy. ppalwc T UNAB SOR-B D b NYPROCARZSON 007157' QCD/MER .SETT/.ING

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TIMER TI'OMS Patented Mar. 19, 194e.

roLYMEarzA'rroN or nrnnooAanoNs Raphael Rosen, Elizabeth, and ober o. slotte:-

beok, Rahway, N. J.,

assignors to Standard Oli Development Company, a corporation of Dela- Ware - Appueaugn oetober 1, 1940,- seriai No. 359,198

z ciaims. .(cn. aso-assisi' This invention relates to the manufacture of olefin polymers, especially those of the type which are suitable for use in the manufacture of mbtor fuels and hydrocarbon `products of similar boiling range. v

.The invention is particularly Vconcerned with-'a practical method for the production of safety" fuels for aviation purposes,` that is, fuels having low vaporPpressures. The manufacture of such fuels has become of great importance in recent years, more particularly because of the tendency towardflying at very high altitudes, where the rapid vaporization of fuels presents a serious problem. This vaporization 'means the loss of the fractions of the fuel having the highest octane boiling range than gasoline as well as'a high flash point.

and a -quality oftrimer product which gives the hydrogenated polymer the highest possible octane rating. These results are accomplished by employing a novel selection and combination o f polymerization factors, such as acid strength, temperature. time of contact, etc. vBy the process of this invention yields of trimer as high as 90% by weight, or higher, based on the isobutylene content of the feed, may be obtained, and the hydrogenated polymer product will have an A. S. T. M. octane number of 98 or higher. The Various reaction conditions required for producing` the best results will be discussed in turn below.

Suitable initial materials for the process of the invention are mainly hydrocarbon mixtures com.. prising chiefly Ci hydrocarbons, such as the C4 refinery cuts obtained in the distillation and v cracking of petroleum, which contain at least 5%.

preferably 10% to 20%, of isobutylene as well as go substantial quantities of n-butylenes and butanes.

Isobutylene itself may of course be used.

The effect ofyarious strengths of acid on lthe proportion of trimer in the nal polymer product was determined for the polymerization of pure Methods have been proposed for-the manufac` 25 isobutylene and a refinery C4 cut. It was found ture of diisobutylene from petroleum refinery C4 cuts containing isobutylene. Hydrosenated diisobutylene is a producthaving a high octane rating and is used for blending with motor fuels of the gasolinev range to improve their octane number.

Such fuels have a relatively high volatility and low flash point and create a fire hazard when used under conditionswhere sparks may be encountered. .'It has been found, however, that hydrogenated triisobutylene has a boiling range of 170-L200 C., which is within the range required for safety fuels and has a remarkably high octane number, i. e.,. of the order of 98 to 99 (ALS. T. M. clear) or even higher. It is therefore well suited for use alone as a safety fuel or in blends 40 of such fuels. The present invention providesa simple and direct means for producingtriisobutylene from a refinery C4 out and for converting the same into the hydrogenated product.

The presentinventionis a modilcationof the .known process of preparing isobutylene polymers from isobutylene or hydrocarbon mixtures containing isobutylene by absorption in sulfuricacid' and heating the. extract so formed. Previous processes of thiskindhave resulted in the formato tion of a major proportion ofdiisobutylene, as in the Rosen and Thomas U. S. Patent` 2,178,808.

VThe present invention provides a process which makes possible the production of the -highest per-s polymers of lisobutylene and n-butylene. product is not desired for the purpose of makingofthe highest grade and quantity of-trimer, in

cases where the 'polymer was to be produced from .a C4 hydrocarbon mixture containing both nbutylenes and isobutylene, was found to be the temperature at which the hydrocarbon mixture was contacted with the acid for the purpose of selectively absorbing the isobutylene. It was found that a quite low temperature, i. e.,`a t least as low as about 0 C., but above the freezing point of the acid used, was -required to give the Vmost satisfactory selective absorption. At higher temperatures large proportions of n-butylene are absorbed along with the i s o buty1eneresulting in the formation of a. considerable amount of co- This the highest octanegnumber safety fuels and their blends, because of the fact that the trimer. fraction of such copolymeriza'tion product, after hydrogenation, shows a poorer octane rating than that of a' product obtained under conditions where only alcomparatively small amount of co- J polymer results.

centages of trimer in the polymerized product 5o The followingtableshows-results obtaine'dby.

absorbing a C4 refinery out containing about 40-50% of total olens and lil-15% of isobutyl` ene. The acid used was of 75% strength, and the amount of the C4 cut used in each case was approximately 80% by weight of the acid present.

The hydrocarbon mixture was gradually intronickel catalyst, and the A. S. T. M. octane number of the hydrotrimer determined. The results are as follows:

TABLE Weight W i ht per ceiet oi percent' Absorpl er trimer N. (A. S Test No. tion ggslinon fraction T. M.) oi

' temp., C. i C H in based on hydrotnmcr fee -ClHa in feed -ao isz 95 9s 1.5-20 152 85 Y 96 40 204 50 94 It is seen that at temperatures above 0 C. the polymer produced is considerably greater in amount than that which would be expected from an extract containing onlyisobutylene, and the excess is largely due to the formation of copolymers of isobutylene` and n-butylene. the percentage of the trimer fraction as well as the quality of the iinal hydrotrimer product is shown to be adverselyaiected by the presence'of lsuch large amounts of copolymer in the polymer product. The employment of low absorption temperatures is therefore an important factor in the' production of the most desirable products.

Further investigation showed that the best results are obtained by heating the acid extract of However,

olefins for a period'of one-half to two hours andat a temperature between about 20 and 100 C.,

the temperature throughout the heating step averaging to 80 C. It was also found that somewhat better yields of trimer are obtained when the extract is heated gradually over this temperature range, with stirring, than when the heating is conducted at a constant temperature intermediate between these limits, e. g., at 60 C. Satisfactory results are, however, obtained by constant temperature heating.

The time of contact of the acid with the isobutylene extract has been found to be a very important factor in the production of the highest yield of trimer. This factor, taken with the strength of the acid used and the temperature of absorption, is a fundamental feature ofnovelty oi the present invention. Experience has shown that for any speciiied strength of sulfuric acid which is used there is va definite range of contact time which gives an optimum yields of the trimer, when the heating is conducted over a tempera- -ture range'of 20 to 100 C. and preferably at 60 to 80 C. Eor example, when 65% acid is used, the best time of contact i's 4 to 5 hours, and with '10% acid, the best time is 2 to 3 hours. However, the best results are secured by using I5-80% acid, and for this strength the preferred time of contact at the polymerization temperature is one-half to 2 hours. If the heating is conducted for periods shorter or longer than those failing within the preferred ranges shown, the yields of trimer are substantially less than those obtained when the preferred times are used.

f It has been found that the yields vof trimer may be increased somewhatfurther by returning to the reaction mixture a portion of the dimer or dimer-codirner mixture obtained on fractionation of the polymer product. In a continuous process based upon this invention, a portion of such lighter polymers may be continuously recycled to the polymerization reactor.` d

A suitable method for carrying out the present invention as a batch process will now 'be described for the case in which aci refinery out is used as the raw material. A suitable mixing and reaction vessel is a Turbo mixer which is 'equipped with a jacket for cooling and heating and with the necessary fittings for introducing the reactants and discharging the reaction products. The C4 renery cut, which is a gas at normal temperatures. is liquefied under pressure and passed into al wellagitated sulfuric acid solution oi' the proper strength. When the amount of the C4 cutis from i to 1.5 times that of the sulfuric acid in the reactor, a, suitable time for passing the hydrocarbon feed into the acid is one to two hours. Provision is made for the release of unabsorbed hydrocarbons which evaporate during the abi sorption process or'on subsequent heating. The temperature of the acid during the absorption step is maintained at 0 C. or lower by means of a suitable cooling medium, such as alcohol, which is passed through the cooling Jacket after passing in contact with al cooling medium, such as dry ice. The evaporation oi' the liquid butane in the mixture assists in maintaining low temperatures. After all of the charge has been passed in contact with the acid. steam is admitted to the heating jacket vat such a rate that the rise of the temperature of the agitated acid extract is approximately 1 to 2 C. per minute until the final polymerization temperature is reached. Moderate superatmospheric pressures, of the order of 25 lbs. per sq. in., are preferably maintained duringthe reaction. At the end of the polymerization step, the agitation is discontinued and the polymer allowed to. separate as a layer above the acid layer. 'I'he polymer is then removed therefrom and washed with an equal volume of 10% aqueous sodium bicarbonate solution and finally with water. In order to prevent the formation of emulsions in some cases, especially. when a more concentrated acid C-80%) is used. the polymer may be washed with a small quantity, say about 25% of an aqueous 50% (by volume) solution of isopropyl alcohol prior to the sodium bicarbonate treatment to remove sulfonation products. 'After drying the purified polymer by contacting with calcium chloride. it may then be passed to a fractionating column to segregate the trimer fraction from the total polymer.

In operations where the initial 'material is substantially pure isobutylene, the hydrocarbon may be introduced into the acid under conditions, such as room temperature and atmospheric pressure, which will not cause premature polymerizaticn or otherwise interfere with the subsequent progress of the reaction.

The method of the present invention may also be utilized in a continuous process for the production or triisobutylene from a C4 reiinery cut.

.Such aprocess is shown in schematic form in the diagram. The hydrocarbon feed gas and a sufiicient quantity of sulfuric acid of proper strength to maintain the acid in the extraction vessel at a constant level are introduced into the extraction vessel i, which is maintained at the desired absorption temperature. The extraction vessel is of, suiicient size to permit sufficient contact between the acid and hydrocarbon before passing to the reactor, and efficient agitation is maintained in this vessel. Unabsorbed hydrocarbons may be removed from lthe extract by raising the temperature suiciently to vaporize such hydrocarbons and allowing the vapors to escape, or by passing the entire mixture 'to a separating vessel (not shown) and allowing the unabsorbed hydrocarbons to separate as an upper liquid layer, which may-be drawn on?. 'I'he acid extract passes next to .the reactor 2,' where the proper polymeriza` tion temperature is maintained, and the reaction mixture is continuously agitated. The size of the reaction vessel and rate of flow into and out of the same are regulated to permit the extract to receive the heat treatment for the required period of time. Any gaseous unreacted hydrocarbons or products of decomposition may be removed through a release valve. The reaction product, consisting of a mixture of acid and polymers, is passed to a settling tank 3, where the product separates into an acid layer and a polymer layer. The acid layer is continuously drawn oli from the bottom of the settlingtank and re turned to the extraction vessel I, where it is reused for further absorption of hydrocarbons. A

portion of the used acid may be drawn oil con-V tinuously or from time to time in order that it may be puriiied or fortified, for example, by the addition of sulfur trioxide, and it may then bereturned to the extraction vessel. The polymerv layer is continuously passed to a fractionating tower which separates the product into (l) unpolymerized. hydrocarbons, (2) dimer and codimer,l (3) trimer and cotrlmer, and (4) heavier polymers. A portion of the dimer and codimer fraction may be returned to the reactor for further treatment, since the dimer maybe converted to trimer by longer contact with the acid.

The reactor for this continuous process may consist of a heating vessel of any convenient form for maintaining a constant temperature, such as a Turbo mixer surrounded by a steam jacket, when a constant polymerization temperature is desired. If it is preferred to provide for gradual heating Charge: Refinery C4"cut parts by weight...I 3,000

H2804 (75%).; do v 2,467

Oleiln content of C4 cut weight percent I1.3 Isobutylene content of C4 cut weight percent-- 14.3 Time of C4 cut addition ;-..h'ours 1.5 Temperature during absorption C-- '-3 to 0 Recovery: l

Spent C4 cut parts by weight- 2,470

Isobutylene do 4 ..n 16.5 :Acid extract r -do 2,942 Material balance weight percent 99 Poymerigation'step -Contact time hours-, l Temperature C-- 20-100 Recovery:

Polymer parts by weight-- 526 llilcid 'l do f 2,366 Material balance v weight percent A 98 ITotal polymer yield (onisobutylene 1 charged). weight percent.;v 122.5- Dimer yield (on isobutylene charged) Weight percent 3.2 Codimer yield (on isobutylene charged) weight percent 17.5 Trimer (plus c'otrimer) yield (on iso= butylene charged) ---weight percent 90.0 Octane number (A. S. 'I'. M.) o f hydro-a genated trimer 99.4

of the extract from room temperature to a convessel until the highest temperature` desired is reached in the last reaction vessel.

The trimer fraction produced as in the above-v described process may be hydrogenated to form a "safety fuel by the use of a suitable hydrowith the nickel catalyst may be carried out in a hydrogenation bomb at-l5002 000 lbs, per sq. in. hydrogen pressure andat a 'temperature of 150 C. during a period of V.1.2-36jhours, using 20 grams of the nickel catalyst for each 600 cubic centimeters of polymer. Other effective catalysts' may be used, but it is important to choose the catalyst and the conditions of hydrogenation so that hydrogenation takes place with a minimum of depolymerization.

One method of carryingfout the present invention may be illustrated by the following example, which is not to 'be considered aslimitative:

EXAMPLE Absorption step l In the abovel example, the polymerization step is carried out by` heating the acid' extract grad-n ually from 20 C. to 100- C. during a period of one hour.

The present invention is not to be considered as being limited in any way by the examples. which are given by way of illustration only, but should be considered'as being limited only by the terms of the appended claims.

1. The method of preparing a hydrocarbon product containing a major proportion of triisobutylene which' comprises contacting a Cs petroleum-refinery cut, containing a'substantlal genation catalyst, e. s.. a iinely dividedactive nickel catalyst. This catalyst is quite susceptible Vto poisoning by impuritiealespecially sulfur, and

the trimer may be purified, for example, by re-1 numng in the presenceoi a caustic solution prior proportion of isobutylene, with a 15%v to ,80% aqueous sulfuric acid solution, heatingthe acid extract so formed at atemperature between 20 and `100 C. and averaginggii to 80C. for a 'period of one-haii to= two'hou'rs inthe'presence 3 to the hydrogenation step. The hydrogenati'onpassing a C4 petroleum refinery cut, containing a substantial proportion of isobutylene, into a y 75% to 80% aqueous sulfuric acid solution in an extraction zone at a temperature at least as low as about 0 C., but above the freezing point of said acid solution, removing unabsorbed gases and continuously passing the extract so formed to a heating zone while the temperature is maintained at 60 to 80 C., continuously passing the product from said heating zone to a. settling zone, where the acid and the polymer formed in said heating zone separate into layers, continuously removing the polymer from the acid layer, continuously returning the acid from said settling zone to said extraction zone, continuously passing said polymer to a fraotionating zone, where it is fractionated into a triisobutylene fraction, a fraction containing diisobutylene and other fractions, and continuously returning a portion of said fraction containing diisobutylene to the said heating zone.

RAPHAEL ROSEN.

OBER C. SIDTTERBECK. y

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