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Patented Nov. 15', 1938 UNITED STATES. PATENT OFFICE ‘ 2,136,785 -.PROCESS FOR POLYMERIZING HYDRO CARBONS William N. Davis, Berkeley, Calm, ?ssig‘niir to Standard Oil Company oi’ California, San Francisco, Calif”, a corporation of Delaware No Drawing. Application March a 1936, Serial No; 67,920 ,. (cl; 196-10) ' 4 Claims. ' This invention relates to a process for the poly merization of normally gaseous ole?ne hydrocar bons to low boiling liquids suitable for use as motor fuels and ‘especially to a. process wherein the polymerization is elfected by an acid-?lm type of catalyst. More particularly the invention pertains to a process suitable for use with a supply particularly pertinent to a‘ process employing this ' type of catalyst that the present invention per tains though its'applicabillty to processes em ploying other catalysts such as the “solid acid” type will be readily appreciated. ' As is well known, the bulk of gaseous ole?nes which are at present readily available for poly of ole?ne containing gas which is subject to wide ‘ merization to liquid motor fuels is produced dur fluctuations in the amount available for poly ing the cracking of petroleum oils. The amount 10 merization. ' of gas produced, its total content of ole?nes and 10. IThe polymerization of normally gaseous ole the proportions of individual ole?nes are found ‘ ?nes to liquids boiling in the range of gasoline I to vary not only with the oil cracked but with ' and suitable as a motor fuel'became economi cally possible with the widespread production of 15 vast quantities of'ole?nes containing from two to ?ve carbon atoms per molecule as a bye-product of the cracking of petroleum and-became par ticularly desirable when it was discovered that such polymers could be produced which could be 20 used as fuel in the modern high compression motors with a high degree of freedom from det onation: Both thermal and catalytic means ve been extensively studied for effecting such poly merization. 25 . 'the extent to which cracking is carried and the speci?c combination of physical conditions under which it is effected. Since for obvious reasons of 15 stock balance and product requirements it is the exception rather than the rule for any commer cial cracking plant to operate continually on the same raw material to e?ect the same degree oi’ cracldng under the same conditions it follows 20' that both the composition and the gross quantity of gas which is available from any such plant to an associated polymerization unit will be quite variable. An even greater ?uctuation in the Many advantages have now been demonstrated > quantity of gas produced is due to the unavoid 25 able intermittence in operation of the individual units of any cracking plant resulting from the to be more or less inherent in the catalytic meth 0d of polymerization and numerous speci?c cata lysts have been developed to meet some particular requirement imposed either by the raw material 30 available or the product desired or both. frequency with which alterations and repairs are ' required by apparatus in such severe service. i The trend toward smaller numbers and increased In general the strong inorganic oxy-acids and size of individual cracking units has still further 30 ‘ their salts or special derivatives have been found accentuated'this latter element 'of ?uctuation‘, ' l to constitute the preferred group of catalytically active materials. Of these, the acids of phos 35 phorus have probably received the widest atten tion and have been most highly developed in the numerous special forms in which they have been applied. Both the liquid and solid acids have been used as such, various of the normal and 40 acid salts have been employed, the liquid acids have been absorbed in highly porous silicious materials such as diatomaceous earth and cal cined to produce the so-called -“solid acid" cata lysts and‘the liquid acids have been ‘adsorbed 45 in .thin ?lms on substantially non-porous inert materials such as glassy quartz to give the “acid ?lm type” catalysts, each group with its own par ticular set of characteristics. Of these several groups of) phosphoric acid 50 catalysts the latter, acid-?lm type, has been found The net- result is thus that a polymerization unit to utilize the fluctuating supply of raw ma terial from any actual cracking plant in an em 35 ciently continuous process for producing a uni form polymer product must either comprise large and expensive reserve storage facilities or possess a de cc of elasticity not reasonably to be ex pecte in the commercial operation of what is at 40 best a critical process. , The object of this invention is broadly to pro vide a method of operating a catalytic polymer ization process employing an acid-catalyst in a smooth and continuous manner on a ?uctuating 45 supply of ole?ne containing raw material with out recourse to the expedient of considerable re serve gas storage. More speci?c objects will be apparent from the description and discussion which follows: I . to possess a combination of characteristics which The polymerization of gaseous ole?ne hydro cause it to stand out as’the most nearly ideal in meeting all of the requirements for vemcient, economical, trouble-free, ?exible commercial op eration. It is to ai'eature of operation which is carbons to yield a liquid product which shall con tain'no polymer higher than a trimer and in certain instances none higher than the dimer is a reaction which is different in many funda 50 2,186,785 Y 2 It has been further found that with phosphoric -‘ , mental respects from the ordinary chemical re action. In order, therefore, to understand the operation of any process for e?ecting such a polymerization these several points of peculiar ity must be clearly appreciated. ' Quite frequently when the supply of raw ma ' terial available for a continuous chemical proc acid there is a concentration range in which the rate of ole?ne polymerization is variable between surprisingly wide limits with only slight changes in the concentration of acid employed as the cat alyst, all other factors remaining constant. The following data are illustrative of this point. They ess is for any reason reduced the rate of ?ow ' were obtained in operation with acid-?lm type through the process is merely reduced in pro . catalysts in which phosphoric acid of the indi cated strength was adsorbed on 10-20 mesh 10 portion and the only result is a reduction in out put from the plant. The extent of an ole?ne broken glassy quartz particles supported in an polymerization is however roughly proportional ‘"rin-ah O to the length of time the polymerizable material is subjected to the polymerizing conditions and appropriate reaction tower. TABLE I Polymerizinq activity of phosphoric acids hence to reduce the rate of passage to accommo date a reduction in the supply of. raw material would obviously result - in over-polymerization. a, When the degree of polymerization permissible in the productionof a given product is limited to dimerization or at most to trimerization any such reduction in rate with its resultant over polymerization is obviously untenable. In many other well known instances-oi’ con tinuous chemical processes a reduction in the 25 temperature of operation may be employed to so reduce the rate of the reaction to-accommodate a reduction in the supply of raw material to the process. The composition of a polymer liquid re sulting from the polymerization of. a mixture of several different ole?nes, such as is contained in a gas produced in the cracking of petroleum, is however directly dependent upon the temperature at which polymerization is effected. Variation‘ is probably due in part to the different propor 35 tions of individual ole?nes which are polymerized at different temperatures and in part to diner ences in the amount of interaction between the several individual ole?nes. In any event 'con stancy of temperature is imperative to constant composition of the polymer product and thus precludes the utilization of reduced operating ' Percent mro. Gigéggys‘t‘l‘glggft' an 0.90 m I 1.60 ?6m 110 15 20 3.50 12. 50 ~ - 13.20 The practically constant rate of polymerization effected by a catalyst in which the acid is at a concentration of from 100 to 110% HIiPOA indi cates the range in which operation would nor mally occur and upon which a plant would be designed to accommodate the maximum quantity of gas ordinarily available. The approximately 30 four-fold change in rate between 100% and 95% H3P04 would then be availed of to compensate for any probable variations in gas supply. It follows from these data, that by the adjust ment of acid concentration in any liquid phos phoric acid catalyst a constant percent polymer ization may be maintained with varying rates of gas passage while the conditions of pressure, tem perature and degree of dilution, which determine the nature and extent of polymerization are held 40 constant. While apparently the form of cata temperatures to compensate for‘ a reduction in lyst employed or the means by which the acid the amount of feed material available to a mixed concentration is adjusted should make no dif ole?ne polymerization process. ierence in the result obtained, from the practical In still other well known chemical processes it standpoint both may be of the utmost importance. 45 is possible to maintain a constant bulk of mate With an acid-?lm type of catalyst in which the rial through a given plant in spite of variations total amount of acid is small, equivalent on the I in amount of reactants available by cycling more or less of some inert diluent. Of the several customary expedients for obtaining constant process operation with variable materials supply this latter is most nearly applicable to a poly merization process though di?‘erences in the degree of dilution of gaseous ole?nes may still somewhat in?uence the nature of the polymer product. The increased cost ofsuch operation per unit of product is also against its adoption wherever other methods are possible. It has been discovered that still another method of compensation may be employed in a‘ process for polymerizing gaseous ole?nes with an acid catalyst and particularly with a phos phoric acid ?lm type catalyst which is subject average to about 3.5 pounds of phosphoric anhy dride per bulk cubic foot of 10-20 mesh support, the small amounts of water required and the 50 ready accessibility of the acid make possible very rapid changes of several percent in acid concen tration by simply varying'the water vapor con tent of the gas to be polymerized. For any given temperature of operation the partial pressure of water vapor necessary to give the acid concen tration desired may be approximated with‘su?l cient accuracy from the data of Table II. _ TABLE 11 to none of the foregoing enumerated objections Mm. 65 and which introduces no new dimculties of. its own. This is based upon the fact that only the rate and not the proportion or degree of polymer ization of mixed gaseous ole?nes is in?uenced by the concentration of the acid employed as cata» 70 lyst. This fact makes it possible to vary the capacity of a given plant to accommodate a var iable supply of raw material merely by appropri-' ately varying the concentration of. the acid cata lyst and without disturbing any of the factors 75 whichdetermine the composition of the product. 60 Water vapor pressure over phosphoric acid solutions Hg. as. 11,204.". ______________________ _99.8 a H|PO|, 72.27 P105 .............. -1(D.5% H‘PO‘, 79.4 0 P10; _____________ _. 140 140 230 o. 0. 0. 400 400 540 400. 0 1(1). 0 70. 0 70 Having determined the temperature and per centage polymerization of the ole?nes contained in' the gas available, which together will lead to the desired polymer product it becomes a simple matter to determine the necessary rate of gas 75 8,186,785 3 passage‘ through a given catalyst chamber to e! ‘iect the proper percent of polymerization. There .in the gas to correspond to other conditions of - operation and the changes necessary to accom after it is‘ possible by varying the concentration of modate changes in such operation may obviously acid in the catalyst in accord with the reaction be arrived at by a similar procedure from‘the ~ rates given in Table I, to maintain the percentage data of Tables I and II. polymerization and hence the nature of the prod It has been found that the heat liberated by uct constant; in spite of variations in the amount the polymerization of normally gaseous ole?nes of gas available. Obviously this may be accom sufllcient that provision must be made for its plished by varying the humidity 01’ the gas more is controlled dissipation in order to permit of close 10 or less inversely with the rate of gas passage. temperature control in a polymerization process. 10 The acid concentration in a ?lm type catalyst has, for instance, been found that when a gas ~follows the humidity of the gas so rapidly that It containing 40% of ole?nes is 95% polymerized when means are provided for‘ correctly control- . suiiicient heat is generated to raise the tempera ling the latter by the amount of gas entering the 15 catalyst chamber the constancy of the polymer ’ ture of the reaction mixture by over 200° F. The removal of this energy'may be advantageously 15 product may be automatically insured. The provided for by dividing the catalyst into two or means‘ for adjusting the humidity of the gas and more series units and inserting ‘an e?icient cool for coordinating the humidity with the amount ing stage therebetween. Such arrangement or gas may obviously be selected at will without 20 departing from the foregoing principles and hence makes possible the removal of already formed polymer product at the same time and ultimately 20 without departing from the spirit of this inven leads to a higher recovery of oleilnes per passage tion. . through the catalyst without excessive over poly It has been round that gases from the crack merization. ‘ ing of petroleum must be puri?ed by washing with Ordinarily the ?rst section of a two unit sys 25 dilute acid, as disclosed and claimed in an ap will contain from 10 to 20% of the catalyst 25 plication Serial No. 07,918 copending herewith tem and will be responsible for about 50% of the to remove traces of alkaline reacting catalyst reaction at the rate of gas passage for which it poisons, usually present, in order to secure long was designed.‘ Ii’ then the rate or‘ gas passage is catalyst‘life. It is also usually desirable to re for any reason materially altered it is imperative so move by an appropriate alkaline wash acid re that the rate of polymerization be altered in com . - acting sulfur bodies such as hydrogen sul?de and merca'ptans, which if allowed to remain are con densed during the polymerization reaction and result in bodies which are di?lcult to remove from the product. . Since both such puri?cation treatments are usually e?ected by means of aqueous solutions 7 they must ‘obviously precede any humidity con trol operation or be made a. part of such opera d0 tion. . nensation in order to prevent a very serious dis so, turbance in the heat balance in the system. By varying the activity of the catalyst in accord with the process oi this invention a method of compensation is provided which prevents any sub 35 stantial disturbance in the heat balance in an operating plant. ving now described my invention which ton sists in a method of controlling the rate of. I The complete process of this invention may now be illustrated by brief reference-to a speci?c ex ample. An olefine containing gas such as de rived‘ from the cracking of “a petroleum oil and containing 30 to 40% total oie?nes'is fractionated to give a cut consisting substantially oi butane and the three isomeric 'butenes. It is then puri~ fled by washing with‘ a 5 to 10% solution of sul furic acid and a solution or caustic soda. Polymerization at a temperature of 300° F., a 50 pressure of about 200 pounds per square inch, a polymerization oi’ normally gaseous ole?ne hydro 40 carbons by a phosphoric acid-?lm catalyst under any given set of operating conditions by con trolling the humidity oi the gas undergoing polymerization: _ I claim: 45 1. In a process for the catalytic polymerization ' ‘of normally gaseous ole?ne hydrocarbons by means or ‘a phosphoric ‘acid-?lm catalyst the \ method of controlling the rate of polymerization at constant temperature and pressure without catalyst acid strength of about 100% HaPO4 and altering its nature or extent to maintain a con a space velocity through the catalyst of about stant product during changes in the time of re 1.0 is desired. The partial water vapor pressure action which comprises the step of regulating the humidity oi'the gas passing the catalyst in a 55 oi the puri?ed gas is accordingly adjusted to cor respond to about 10.2 millimeters olmercury im ratio inverse to the rate oi’ age. ‘ 55 mediately prior to passing‘ the gas over the'catam 2. In a process for the catalytic polymerization lyst. It is soon found however that the rate 01’ of norlly gaseous olefine‘ hydrocarbons by . gas- production at the cracking plant has been means of ‘a phosphoric acid ?lm catalyst the 00 reduced by about 20% and consequently there. method of quickly altering the e?’ective capacity is sumcient gas available to maintain only a space ' of a given plant to accommodate changes in the velocity of 0.80 through the catalyst which liner available supply ‘of ole?ne containinggas which mltted without any compensating change will comprises the step'oi' regulating ‘the’v partial pres give a considerable proportion of liquid polymer sure of water vapor associated with said ole?nes 65 boiling above the range which is permissible in in a ratio inverse to the quantity of gas entering the particular product desired. The water vapor the catalyst unit. 05 . pressure in‘ the gas is accordingly adjusted’to 3. A process for‘ the catalytic polymerization about 25.0 millimeters. of mercury which quickly of normally gaseous ole?ne hydrocarbons to brings the acid in the catalyst to about 98% liquids which comprises passing a gas containing 70 HaPOr' having a polymerizing-activity of approx» said oleilnes over a catalyst consisting. of a thin imately 0.8 that 01' 100% acid.‘ Operation may film of phosphoric acid adsorbed on a non-porous 70 thus proceed with the reduced ?ow oi.’ gas and the nature of the polymer product remain-un ch inert support maintained under polymerizing con ditions of temperature and pressure and holding ‘said temperature‘ and pressure substantially con e appropriate partial water vapor pressure stant while varying the supply of said ole?ne con _ ged. ' r 4 2,136,785 taining gas and simultaneously inversely varying its water vapor content. 4. In a process for the catalytic polymerization of normally gaseous ole?ne hydrocarbons to 5 liquid motor tuelsby means of a phosphoric acid ' ?lm catalyst the method of maintaining the na ture and extent of polymerization constant while varying the time of reaction at constant tempera ture and pressure which consists in varying the partial pressure of water vapor in the gas mix ture passing over the catalyst in inverse ratio to the rate of passage. WILLIAM N. DAVIS.