US2354641A - Treatment of paraffin hydrocarbons - Google Patents

Description

July 25, 1944. c. G. GERHOLD TREATMENT OF PARAFFIN HYDROCARBONS Filed March 30, 19110 www mm fx J.. ww .www

Passau Juzs, 1944 TREATMENT F PARAFFIN HYDBOCABBCNS Clarence G. Gex-hold, Chicago, lll., assigner to Universal Oil Products Company,

ammo m0 a corporation of Delaware v application March 3o, 1940, serial No. 326,870 o claims. (ci. zoo-'mm This invention relates to the treatment of branch-chain parailin hydrocarbons with olens.

In a more specific sense, the invention is concerned with a process for the preparation of motor fuels by alhlating isoparafllns with oleilns in the presence of a strong acid, 4particularly concentrated sulfuric acid or anhydrous hydrogen iluorlde.

Cracking processes which are operated principally with the object of producing gasoline from heavier land less valuable petroleum fractions incidentally produce considerable yields of nxed gases, consisting of hydrogen. methane, ethane, propane, and butane, as well as ethylene, propene and butenes invarylng quntities and proportions. In many cases these gases are considered to be valuable merely as fuel, although at the present time some of the olennic constituents are utilized for the manufacture of hydrocarbon derivatives on a commercial basis. There is also a large production of ilxed gases in connection with the production and rening of petroleum. Large amounts of parafdnic gases occur as nat- `ural gas and well or casinghead gases. These petroleum gases are often utilized only as fuel and from the standpoint of the oil renner, who is primarily concerned with the manufacture of gasoline and lubricating oils, these gases are mainly considered as waste material, so that considerable experimentation has been conducted to iind methods for converting them into liquid products with practical emciency.

In some cases it may be desirable to decrease the volatility of a certain hydrocarbon Imotor fuel. This may be accomplished by removing a portion of the light ends by distillation so as to separate such normally liquid hydrocarbons as pentanes and hexanes. The branch-chain members of these two groupsA of compounds may be reacted with olens to form isoparamns of higher molecular` weight. weight isoparaflins may be incorporated into the motor fuel, resulting in a decreased volatility as well as an increased volume.

One process in common use at the present time for the conversion of these lighter hydrocarbons into motor fuel consists in the interaction of isoparamns with olens in the presence of strong acids such as sulfuric acid or anhydrous hydrogen nuoride. Under appropriate conditions the reaction,

isoparailin+olen=isoparailin' takes place with a minimum production of olefin polymers and heavy products. A method for op- These higher molecular erating this process well-known to the art uses sulfuric acidas a catalyst and may be brieiiy described as follows:

Isop are allowed to react with oleilns in the presence of sulfuric acid and a sumcient length of time under the desired conditions of temperature until the olenns have been substantially removed. Isobutane is the isoparai'lin commonly used although higher molecular Vweight isoparamns will also undergo the reaction referred to. The higher molecular weight isoparailins are themselves valuable constituents of the motor fuel and are used for alkylation purposes only in the case where their supply is in excess of that needed for volatility requirements. Oleiins from Cs to C4 inclusive may be used, although the common charging stocks are often limited to Ca and C4 oleilns. The acid in contact with the hydrocarbons is usually at a concentration somewhere between 88 and 93% titratable acidity. It is kept at this ngure by continuously withdrawing part of the used acid and supplying make-yup acid of 96 to 100% strength. The charging stock is commingled with an isoparailln recycle such that the isoparailln to oleiin ratio in the hydrocarbon feed to the acid-hydrocarbon mixture in the reactor is approximately 5 to 1. 'Ihis ratio insomecasesmaybeassmallas3to1,and others as high as 10 to 1. It is somewhat dependent upon the oleiins being used.

'I'he process is operated on a continuous basis, complex mixtures of unreacted isoparaflins, motor fuel and heavier products being withdrawn at the Vsame rate as fresh charging stock is being supplied to the reactor. 'I'he oleiln-isoparamn alkylation process may be thought of as an absorption of olen in the acid phase to form an olen-acid ester which subsequently reacts with the isoparailln to form a second isoparaflin of higher molecular weight. In order to keep the competing olefin polymerization reaction at a minimum, the ratio of isoparaillns to.olens in the reacting zone is kept high. At the entrance to the reactor, it is common to have present 100 moles of isoparamn for each mole of olefin being supplied in the charging stock. This ratio may be varied from to 120. The pressure used in the system must be suiiicient to keep all constituents in the liquid phase. Pressures higher than this are of no particular aid to the process. The pressure necessary to prevent vaporization in the system depends both on the composition of the feed and on the temperature used. Temperatures between 32 and 50 F. are quite satisfactory and are commonly used. Satisfactory results have been obtained with temperatures as high as 100 F. The ratio of acid to hydrocarbon is usually 1 to 1 but may vary from 0.7 to 1.0 to 2 to 1. The reactor used in the process consists quite often of a tower equipped with orifice plates, although any method that satisfactorily contacts two immiscible liquids may be used.

It has been shown that anhydrous hydrogen fluoride is also a very effective catalyst in promoting the alkylation of isoparafllns with oleiins. Either sulfuric acid or anhydrous hydrogen uoride may be used in the present invention, although their use is not intended to be on an equivalent basis.

The present invention comprises a modification of the previously described process of alkylating isoparafllns with oleiins in the presence of concentrated mineral acid. The essential feature of this invention consists in a separate step in which the used mineral acid is reacted with isoparaflins. It is well-known that the acid layer in alkylatlons contains dissolved in it complex hydrocarbons and their reaction products with acid, which substances tend to destroy the acid and decrease its period of usefulness. My invention is intended primarily to increase the life of the acid as well as to convert the substances pres-- ent in it to useful products.

In one specific embodiment, the present invention comprises catalytically interacting isobutane and normal butenes in the presence of concentrated sulfuric acid using a large excess of isobutane to butenes, continuously removing a portion of the acid-hydrocarbon mixture, separating the acid and hydrocarbons, directing the latter to a separating zone for separation into isobutane, normal butane, alkymer of the motor fuel boiling range and heavier products, reacting the used acid with isobutane in a separate reactor and returning the mixture of isobutane and regenerated acid to the alkylating zone.

To indicate in general the type of process iiow which characterizes the present invention, the attached drawing has been provided which indicates diagrammatically by the use of conventional interconnected units drawn in side elevation an arrangement of plant apparatus in which operations typical of the process may be carried out.

Referring now to the drawing: The charging stock consisting of a mixture of oleflns, isoparafns, with or without the unreactive normal parailins as diluents, is supplied to the system through line I, valve 2 to line 3 wherein it is commingled with the recycle stock of acid and hydrocarbons arising in a manner to be described later. This combined feed and recycle stock is directed through cooler 4 wherein it passes in indirect heat exchange relationship with a cooling medium supplied by line 5, valve -5 and removed by way of line 1, valve 8. The

cooled mixture enters reactor I by way of line 5. This reactor may contain orice plates or be of any general construction that will promote thorough mixing of the acid and hydrocarbon layers. The material leaves reactor I0 by way of line II, a portion being diverted through line I2, valve I1 into settler I8, where a separation of the two phases takes place. The remainder of the mixture leaving reactor I0 is removed from line II through line I3y and valve I4, where by means of pump I5, it is commingled with fresh feed entering the system through line I aspreviously described. The used acid separated from the hydrocarbons in settler I8 is removed by way of line 58, valve 38 and is in part returned to line I5 by way of line 63, valve 54 and in part directed to line 38 wherein it is commingled with isobutane obtained through line 23. This mixture of acid and hydrocarbons is commingled with a recycle stock obtained from reactor 48 through line 49 and valve 50. The resulting mixture of acid and hydrocarbons is directed by means of pump 44 through valve 45 into line 59 from which it enters cooler passing in indirecr heat exchange relationship with a cooling medium supplied through line 53, valve 54 and rermoved by way of line 55, valve 55. The cooled mixture enters reactor 48 by means of line 41 Reactor 48 may be of the same general construction as reactor I0. In this reactor the iso-butane enters into chemical reaction with the complei.Y hydrocarbon constituents of the acid layer. Afte' sufficient interaction, the mixture of acid am hydrocarbon leaves the .reactor by way of lin 49, valve 50. A portion is recycled through liny 38 while the remainder is directed into line 5 containing control valve 52 from which it passe` to line I5. The mixture of hydrocarbons anc. regenerated acid leaves line I5 entering line I3, wherein it becomes part of the recycle material of reactor Ill. Fresh acid may be admitted to the system through line 5I containing control valve 52.

The hydrocarbon layer obtained in separator I8 is removed by way of line I8, valve 20 and supplied to fractionating column 2l. This co1- umn may be of the plate and bubble-cap type or of any general construction known to the art for the rectification by distillation of liquid mixtures. This column removes iso-butane as an overhead product which, after returning a portion to the column for cooling and reflux, is removed through line 23 containing control valve 42 and directed by means of valve 43 to line 39, wherein it isl commingled with used acid obtained from separator i8 as previously mentioned. If desired, a porltion of this iso-butane may be directed from line 23 to line 51 wherein it passes through valve 58 into line I5 being commingled therein with a hydrocarbon-acid mixture obtained from reactor 48. Column 2| is equipped with closed heating coil 22, by means of which heat may be supplied for conducting the necessary vaporization process. The Vdeisobutanized hydrocarbons are removed from column 2i, by means of lin'e 24 and after passing through valve 25 enter the second fractionating column 25. The construction of this column may be similar to that of column 2| and is intended primarily to remove any normal butane present from the system. The normal butane is removed from column 25 as an overhead product through line 28, valve 29 and after returning a portion to the column for cooling and reflux, the remainder may be sent to storage. Column 26 is provided with heating coil 21. The

higher-boiling hydrocarbons consisting principally of alkymers, leave column 25 through line 30 containing control valve 3I and are directed to column 32 provided with heating coil 31. The purpose of column 32 is to separate the alkymer of motor-fuel boiling range from the heavier boiling hydrocarbons. The alkymer of motor-fuel boiling range is removed from column 32 as an overhead product through line 33 containing control valve 34 and sent to storage. The alkymer boiling above the motor fuel range'is removed 'as a bottoms product from column 32 through line 35 containing control valve 35.

The following example isintroduced to indicate the character of the results obtainable by the use of the present process, although it is not intended to limit the scope of the process in the exact correspondence with the data submitted.

A residual gas formed by the removal of the isobutylene in a butane-butene fraction by sulfuric acid polymerization may be charged to the process. A typical charging stock of this nature may have the following composition: 18.5% normal butenes, 25.5% iso-butane, 54.8% normal butane and 1.2% pentanes. After commingling sufficient iso-butane obtained from the de-isobutanizer so as to obtain a to 1 isobutane-normal butene ratio, the combined feed and recycle stock may have a composition of 11.1% normal butenes, 55.3% iso-butane and 32.8% normal buy tane and 0.7% pentanes. This combined feed and hydrocarbons may be mixed with an equal volume of sulfuric acid with a concentration slightly in excess of 93%. Thefresh acid fed into the system may have a composition of 98% but after mixing with the used acid, the concentration may be slightly over 93%. The acid and hydrocarbons are continuously removed from the reactor and sent to a cooler to remove the exothermic heat` of reaction. 'Ihe amount of time spent in the reactor is approximately 1.2 minutes per pass and the total residence time may be approximately minutes. Under these conditions 5% of the material leaving the reactor is removed to a separator. Fresh hydrocarbons are supplied at a rate equal to that at which they are being removed from the first reactor system as described above. The acid obtained in the separator will be commingled with an equal volume of iso-butanes and the mixture supplied to the second reactor system. The second reactor is designed in such a manner that the total residence time of the acid and hydrocarbons will be approximately one hour. A recycle-to-removal ratio of 10 to 1 is used. The titratable acidity of the acid is increased from 93.0 to 93.3 by this isobutane treatment. The system operates with an acid consumption of 0.42 pound of acid per gallon of alkymer produced.' The lhydrocarbon layer of tained in the separator is de-isobutanized and isobutane commingled with the used acid as, shown in the figure. After removal of the isobutane, the normal butane is removed in a second fractionating column and the debutanized product then sent to a fractionating column for separation into motor fuel and heavy bottoms. The amount of heavy bottoms may be approximately 6.5% of the total weight of the alkylate. The alkylate sent to storage contains approximately 86% Ca and 14% lighter hydrocarbons. It has an initial boiling point of 135 F. and end point of 250. The acid heat will be under 20 and the bromine number less than 0.1. The octane number will be approximately 93 by the C. F. R. motor method.

I claim as my invention:

1. An alkylation process which comprises reacting an isoparaflln with an olefin in the presence of a mineral acid alkylating catalyst in a reaction zone, removing from said zone a mixture of hydrocarbon reaction products and acid catalyst, separating said mixture into a hydrocarbon layer and an acid layer, returning a portion of the acid layer to said reaction zone, subjecting another portion of said acid layer, containing complex hydrocarbon constituents, to reaction with an isoparailln in the substantial absence of added oleflns for a sufilcient time to regenerate this portion of the acid catalyst, and supplying the thus regenerated acid to said reaction zone for further use therein as an alkylating catalyst.

' 2. An alkylation process which comprises reacting an isoparafn with an olefin in the presence of a mineral acid alkylating catalyst in a reaction zone, removing from said zone a mixture of hydrocarbon reaction products and acid catalyst, separating said mixture into a hydrocarbon layer .and an acid layer, returning a portion of the acid layer to said reaction zone, subjecting another portion of said acid layer. containing complex hydrocarbon constituents, to reaction with an isoparamn in the substantial absence of added olens for a sufficient time to regenerate this portion of the acid catalyst, and supplying the resultant reaction mixture of hydrocarbons and regenerated acid to said reaction zone.

3. The process as defined in claim 1 further characterized in that said catalyst comprises sulfuric acid.

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