US2286183A - Alkylation of isoparaffinic hydrocarbons - Google Patents

Description

Patented June 16 1942 UNITED STATES PATENT OFFICE ALKYILATION 0F ISOPARAFFINIC HYDROCARBONS William E. Bradley, Los Angeles, and Karl J. Korpi, Palos Verdes Estates, Calif., assignors to Union Oil Company of California, Los Angeles, Calif., a corporation of California No Drawing. Application May 2, 1938, Serial No. 205,532.

, 2 Claims. The present invention relates to the treatment of hydrocarbon oils, and refers to the manufacture of parafiinic hydrocarbons of a branched chain type particularly suitable for use in automobile and aviation engines. In a more specific sense, the invention comprises a process for the combining of isoparafiinic hydrocarbons of relatively low molecular weights with olefinic hydrocarbons to produce branched chainparafiinic hydrocarbons of higher molecular weight, boilingv within the gasoline range and particularly valuable as motor fuels or constituents thereof in view of their unusual anti-detonating characteristics. The invention further comprises the use of special catalysts .and conditions of operation i or the manufacture of these valuable compounds.

Since the present process is directed to the efficient utilization of certain olefinic and parafiinic hydrocarbons, particularly those found in commercial gas mixtures, and since the process produces hydrocarbons of high anti-knock value for use as motor fuels, the following discussion is given for the purpose of describing the character of these materials.

Olefinic hydrocarbons occur along-with pa-rafflIllC and unsaturated hydrocarbons in various commercial hydrocarbon mixtures. For example,

olefins are encountered in the products resulting from the cracking of petroleum, in gas making processes, and as by-products in various chemical industries. Also, they may be produced by the simple dehydrogenation of corresponding paraffim'c hydrocarbons. In general, olefinic hydrocarbons are more chemically active than other classes of hydrocarbons. Thus, even under mild catalytic influences, olefinic hydrocarbons exhibit a high reactivity in their tendency to polymerize and form substances of higher molecular weight. On the other hand, parafiinic hydrocarbons, such as isobutane and isopentane, normally occurring in natural gas or similarly related materials, are usually considered to be more or less chemically inert and are incapable of polymerizing.

It is one of the objects of the invention to provide for a more effective utilization of certain of the isoparaffinic and olefinic hydrocarbons to produce valuable derivatives thereof. It is a further object of the invention to provide for a more efiective utilization of the low boiling isoparafiinic hydrocarbons, namely isobutane, isopentane, and

isohexane, and of certain olefinic hydrocarbons to produce branched chain hydrocarbons having high anti-detonating characteristics and boiling substantially within the gasoline range. The process described herein may also be applied to individual olefins and isoparaflins as wellas to their mixtures.

The reaction between one or more isoparaffinic molecules and one or more olefinic molecules produces an alkylated' paraflinic molecule of a branched chain type. This product is herein referred to as alkymer in order to distinguish it from a polymer which is the product resulting from the interaction of two or more olefinic molecules. Theoretically, the reaction between an isoparafiin and an olefin in the presence of a suitable alkylating catalyst is of a simple character. Thus, the combination which takes place when isobutane is chemically .combined with a butene may be expressed as follows:

isobutane butene octane The above equation shows the union of one molecule of isobutane to one molecule of butene to produce one molecule of iso-octane. Similar reaction equations may be written for the alkylation of the above or other isoparafilns with various olefins.

As will be'tbrought out more fully hereinbelow, the term alkylation as employed herein includes not only the simple chemical combination of isoparafiin molecules with the olefinic molecules introdu ed into the sphere of reaction, but also the union between the specified isoparafi'inic and olefinic molecules formed in situ as by the splitting of relatively larger molecules.

- Olefins, when subjected to proper reaction temperatures and pressures in the presence of a suitable catalyst, such'as sulfuric acid, tend to form polymers. In fact-this tendency to polymerize;

at least under certainponditions, occurs in preference to alkylation so that if a mixture of isoparaffinic or even cyclic hydrocarbons and olefins strong acid tends to react to a certain degree with the hydrocarbons treated, this side reaction causing the formation of by-products which progrese and the higher olefins.

sively decrease and may finally completely inhibit the catalytic activity of the acid.

It is therefore the main object of the present invention to provide a process wherein alkylation of the isoparaflins with the olefinic hydrocarbons shall be favored in preference to the polymerizationof theolefins introduced into the reaction zone for the purpose of combining with the iso- It is a further object paraffinic hydrocarbons. of the invention to provide a process wherein valuable motor fuel fractionsv having high antidetonating characteristics may be produced by efficient alkylation'of low boiling isoparafiinic hydrocarbons with normally gaseous and liquid olefins above ethylene and preferably having not more than about 12 carbon atoms in the molecule.

It is a still further object to provide a process of I the type described wherein the alkylation reaction isfavored and wherein substantially no polymerization of the olefins occurs.

'It has now been found that the above and other objects may be attained by adding certain oxidation inhibiting or mitigating agents to the alkylating catalyst. covered that the oxidation inhibiting or reaction mitigating agent to be employedin connection.

with the alkylating catalyst may be selected from the polyhydric alcohols, such as glycols or glycerine, mixed polyhydric alcohol ethers, for ex} ample the mono-l dior tri-butyl ethers of ethylene or di-ethylene glycols, as well as from the higher boiling aliphatic ethers: such as diamyl ether, or mixtures thereof. These substances, or their mixtures, may be employed in connection with various alkylating catalysts such as sulphuric acid, benzene sulphonic acid, phenol sulphonic,.

etc. Particularly, the described agents find util- It has further been dis-1 boiling olefins since the alkylation reaction be- .comesunfavorable when such very high boiling olefins are employed, Thus, it is preferable,

although not absolutely essential, to use fractions having olefins of not more than 12 carbon atoms per molecule.

It is to be further understood that the reference to isoparaflini'c and olefinic hydrocarbons includes the use of these hydrocarbons individually, in mixtures with other hydrocarbons of the particular class or mixtures thereof with other hydrocarbons.

In one of its broadest concepts, theinvention may therefore'be stated toreside in reacting isoparaffinic hydrocarbons of the type of isobutane, isopentane andisohexane, with normally gaseous or normally liquid olefinic hydrocarbons, or with both types of olefins, in thepresence of an alkylating catalyst containing oxidation inhibiting or reaction mitigating agents, whereby the olefins are caused to react with 'the isoparaflins in preference to the polymerization of the olefins, and

whereby the tendency toward the.occurrence of side reactions is reduced or eliminated and the alkylating activity of the catalyst prolonged. The invention further resides in the above process in which the products of reaction predominate in alkymers boiling within the gasoline range and are substantially free from products of polymerization. a

The invention further resides. in reacting the lower isoparaflinic hydrocarbons with the afore-' mentioned olefins in the presence of an acid ity when employed with the stronger acid catalysts, such as strong sulphuricacid, which possess the above described oxidizing tendencies.

Various proportions of the oxidation inhibiting or reaction mitigating agents may be employed.

However, relatively small proportions, for, ex-

ample proportions ranging from about 1% to 10% of the total catalyst employed, are adequate to reduce and even eliminate the tendency toward undesirable reactions. These relatively small quantities of the above agents furthermore increase the alkylating activity of the catalyst in that the products of reaction contain greater quantities of alkymers-boiling within the gasoline range as compared to the yields produced by the use of the given catalyst alone. Also the life of the alkylating catalyst of the abovedescribed type is prolonged by the addition thereto of the described oxidation inhibiting or mitigating agents.

Th term isoparamns? and isoparafllnic hydrocarbons as employed in the specification and claims, relate to the lower 'isoparafiinic members,

namely isobutane, isopentane and isohexane. It has been found that the rates of alkylation of,

those isoparaflinic hydrocarbons, maintaining other conditions equal, are not the same. Thus, the rate of alkymer formation when isopentane is employed is considerably slower than the rate of alkylation of isobutane, while the alkylation rate of isohexane is even still lower.

As to the terms .olefins and olefinic hydrocarbons, they relate both to the normally Baseous olefins which comprise the hydrocarbons I between about propylene and pentene s, and to the normally liquid olefins such as the hexanes It is to be noted, however, that it-is not desirable to employ very high catalyst'containing an'oxidation inhibiting and reaction mitigating agent such as polyhydric alcohols, mixed polyhydric alcohol ethers, and relatively higher boiling aliphatic ethers. The in- .vention also includes the use of relatively small proportions of the above agent or agents, quan--' tities ranging from about 1% to 10% of the total catalyst employed being sufficient inmost cases.

The invention still further includes the alkylation of isoparafllnic hydrocarbons of less than seven carbon atoms per molecule with the described olefins in the presence of a catalyst comprising a mixture of a strong acid, such as sulfuricacid of to HaSOi content, with a suitable oxidation inhibiting and reaction mitigating agent, said catalyst promoting the combination of said'oleflns with the isop'araflinic hydrocarbons to produce higher boiling parafllnlc hydrocarbons of a branched chain type boiling within the gasoline range, having high antiknock I preference to the polymerization of said olefins,

and whereby the tendency toward the occurrence of sidereactions is reduced or eliminated and the alkylating activity of the catalyst is prolonged.

Furthermore the invention in one of its embodiments also includes the realization of the above reactions substantially in the liquid phase. This can be realized'by conducting the reaction at pressures sufiicient to maintain the reacting hydrocarbons in a liquid state.

The following examples are presented to show the advantages obtained when using as a catalyst a material comprising a mixture of sulfuric acid with a suitable mitigating agent, such as for example di-amyl-ether. In these experiments the isoparafllnic fractions employed comprises a narrow cut obtained from the stabilization of natural gasoline and an analysis of this fraction indicated that it consisted of approximately 89% isobutane, 3% normal butane and 8% propane. It is obvious that the isoparaflinic fraction to be alkylated according to the present invention may consist of hydrocarbons other than isobutane such as, for example, isopentane, or may comprise a mixture containing these and other isoparafilns.

The specific olefin-containing fraction employed in the experiments was derived from petroleum cracking operations and had substantially the following composition:

Percent by volume Is is thus seen that the above olefin-containing gases contained about 49.0% unsaturates, exclusive of ethylene, the ratio of propylene to the butylenes being about 1:l.-

Two runs were made in one of which sulphuric distillate was selected because it satisfied the United States'Army' Air Corps Specification No.

of liquid Ethylene 0.57 Ethane I 4.50 Propylene 24.27 Propane 30.28 Isobutane 7.33 Isobutylene 12.63 Normal butylene 12.10 Normal butane 8.32

acid of 90.9% H2304 content and the other of which sulphuric acid of the same strength to which 5% of di-amyl-ether has been added were was maintained in a state of violent agitation.

After all of the .olefinic stock had been added, agitation was discontinued, the acid phase allowed to separate, andthe hydrocarbon product withdrawn and stabilized. This stabilization may be obtained by distilling the hydrocarbon .phase in a reflux column under pressure .to a

temperature of about to F. and a pressure of about 15 pounds absolute. The residual fraction comprised a hydrocarbon product predominating in products of alkylation boiling within the gasoline range.

In the experiment in which 90.9% sulfuric acid alone was employed as the catalyst, the stabilized reaction product comprised 142% of the volume of the olefins present in the charging stock. Of.

this product approximately 88% by volume distilled over at 310 F., the resulting distillate,

equivalent to about by volume of the olefinsv originally charged,- containing no products of polymerization. The 310 F. end point of the 2-95 for aviation gasoline.

On the other hand, the yield of the stabilized of employing as 'a'catalyst a mixture of sulfuric acid with a suitable mitigating agent rather.

than sulfuric acid alone. I

Thus, the sulfuric acid diamyl-ether mixture allowed; the realization of approximately 6% more aviation gasoline than was obtained by the useof the sulfuric acid alone.

When the reaction is to be effected in theliquid phase, it is preferable to maintain a concentration of isoparafiins in excess of .the quantity theoretically necessary to combine with the olefins. This excess should exist 'duringthe whole course of the reaction. Therefore, in the preferred embodiments of the invention the isoparaflins enumerated above, or'their mixtures,-

are first commingled with the catalyst containing the described oxidation inhibiting and reaction mitigating agent. -,Thereafter, the olefins are slowly and gradually introduced into the mixture. The presence of an excess of isoparai'fins, combined with the relatively slow and gradual addition of the olefins is necessary to prevent any local over-concentration of the olefins, this over-concentration favoring the undesirable polymerization of the olefins instead of the alkylation of the isoparaffins. In other words, the constant presence of an excess of isoparaflinic molecules increases the chances of contact of each activated olefin with an activated isoparafiin molecule. Simultaneously, the relatively slow addition of the olefins, together with the agitation of the mixture, tends to disperse the olefin molecules, thus decreasing their con-' centration and also favoring the possibility'of the alkylation reaction to take place in preference' to the polymerization of the olefins.

The above disclosure is presented in connection with the alkylation of isoparafiins with olefins, and emphasizes the simple addition of the relatively low molecular'weight normally gaseous olefins (preferably above ethylene) to the specified isoparaifins. In addition it was discovered that in reacting the isoparaflins withnormally liquid olefinic hydrocarbons the reaction product comprises a large proportion of saturated branched chain hydrocarbons boiling within the gasoline range. Such hydrocarbons evidently could be formed by an initial scission of at least one of the original reacting hydrocarbons into a plurality of molecules of lower molecular weight, and the subsequent reaction of these lower molecular weight hydrocarbons to produce the branched chain paraffinic hydrocarbons- The same result may also be due to a simple addition of the introduced qlefinic molecules to the iso-, paraffinic molecules, followed by a scission of the product. Specifically, this alkylation reaction, therefore, may be called a cracking alkylation reaction in order to distinguish it from the straight or simple addition of an introduced olefin to the isoparaifin, as this has been described hereinabove.

The cracking alkylation? reaction may thus be described as includingthe step of reacting olefin molecules with isoparaflinic molecules to produce one or more parafiinic alkymer molecules which have molecular weights of less than that which would be obtained providing the reaction were of the simple addition type in which, as previously stated, an olefinic m'olecule'introduced into the of the catalyst containing the oxidation inhibit-' ing and reaction mitigating agent, to produce both the simple alkylation of the isoparaflins by have a lower molecular weight than would be the olefins added, and the cracking alkylation in I which, as stated, alkymers are produced which obtained by simple addition of an olefin to an isoparaffin. The higher molecular weight olefins, for example above dodecenes, however ap pear to be undesirable since the products of reaction, when using these high molecular weight olefins, contain excessive percentages of polymers boiling above the gasoline range.

The term gasoline boiling range is used here to denote the average boiling range of fuels used in automobile engines. Generally speaking, such a gasoline has an initial boiling point of about 100 F., and a maximum or end point of around 425.F, The term atmospheric pressure refers to'pressures in the neighborhood of 760 mm.'of

mercury, while atmospheric or room temperature relate to temperatures in the vicinity of In carrying out the invention the apparatus used and the'conditions of operation chosen in respect to temperature, pressure and proportions olefins and/or isoparaflins produced by special chemical methods or by a suitable fractionation of mixtures in which they occur.

Many other pertinent and equally different embodiments may be made by those skilled inthe art, without departing from the spirit and scope hereof, and it is therefore understood that there is no intention to be limited by the specific embodiments disclosed herein except as defined bythe appended claims.

We claim:

L'A process for producing motor fuels which comprises reacting isoparaflinic hydrocarbons of less than seven carbon atoms per molecule with olefinic hydrocarbons having more than two carbon atoms per molecule in the presence of an alkylating catalyst and diamyl ether.

2- A process for forming alkylated branched chain paraflinic hydrocarbons boiling within the gasoline range and substantially. free from polymers, which comprises reacting isoparafiinic hydrocarbons of less than seven carbon atoms per molecule with normally liquid olefins preferably of less than thirteen carbon atoms per molecule, in the presence of a catalyst mixture containing strong sulfuric acid and diamyl ether.

WILLIAM E. BRADLEY. KARL J. KORPI.