US2393895A - Treatment of hydrocarbons - Google Patents

Description

Jan. 29, 1946.

J. R. FLEMlNG TREATMENT OF HYDROCARBONS Filed July 24, 1944 Patented Jan. 29, 194e UNirED STAT-Es Para orsi TREATMENT F HYDROCARBONS James R. Fleming, Port Arthur, Tex., assigner to The Texas Company, New York, N. Y., a corporation oi Delaware Application July 24, 19414, Serial No. 546,321

8 Claims. (Ci. 260-67l) This invention relates to the treatment of hydrocarbons and particularly the separation of normally gaseous hydrocarbons from-mixtures containing them with subsequent conversion into valuable products` useful in the manufacture of gasoline and other products.

The invention contemplates a method of separating olens from gaseous mixtures and separately treating the oleiins to convert them into valuable products. It also contemplates a combination process for the manufacture of gasoline of high anti-knock value and having other desirable characteristics.

In accordance with the invention, normally gaseous hydrocarbons comprising olens having from 2 to 4 carbon atoms per molecule are lobtained from the products of hydrocarbon cracking and the olelnic constituents thereof are separately treated to convert them into valuable products. Thus, a C4 fraction and a Ca and lighter fraction are obtained. The C4 fraction containing` normal butylenes, isobutylene and paraflins is subjected to contact with concentrated sulphuric acid in the presence of a low boiling isoparaiiingsuch as isobutane under alkylating conditions so that normally liquid alkylated hydrocarbons boiling within the range ofgasoline are produced.

Sulphuric acid which has become spent as a catalyst for the alkylatlon reaction is then employed to eliect selective absorption oi' ethylene from propylene in the Ca and lighter fraction.

l The resulting ethylene acid mixture is subjected.

to elevated temperature so as to eiiect partial stripping of ethylene, thereby obtaining ethylene in substantially pure form and also producing a partially desorbed ethylene acid mixture.

The partially desorbed acid mixture is employed to extract propylene from the residual gases advantageously under conditions such that the residual ethylene contained in the acid mixture is displaced from the acid by propylene.

The resulting propylene acid mixture may be disposed of by subjecting it all or in part to elevated temperature so as to liberate propylene in substantially pure form. On the other hand, all or part oi' the propylene acid mixture may be subject to hydrolysis under conditions effective to convert the propylsulphate into alcohol.

Preferably the propylene rich acid is passed to an aromatic alkylation zone wherein the mixture is subjected to contact with'a low boiling aromatic hydrocarbon such as benzene, toluene or xylene in the presence of some free acid so as to eilect prcpylene. In this way cumene is prepared by alkylating benzene with the propylene y while cymene is prepared byreacting toluene with the propylcne.

Both cumene and cymene are desirable constituents of high grade aviation gasoline. These compounds are blended with gasoline so as to increase the rich mixture performance and thus permit obtaining more power from the fuel during take-oir. These compounds may be mixed with the aforementioned alkylated gasoline obtained by alkylating Ci oleflns with isobutane and may be blended in the proportion of about 5 to 15% by volume.

In accordance with the invention, the aromatic hydrocarbon or hydrocarbons used in the aromatic alkylation may be derived from cracked naphtha or from hydro-formed naphtha.

The spent acid from the aromatic alkylation operation ls advantageously passed to an acid concentrating zone or unit wherein the concentration is brought back to 94 to 100% H2804. The reconcentrated acid is then recycled to the first mentioned alkylation unit Vwherein C4 olens are reacted with isobutane. Some of the spent acid from the aromatic alkylation operation may be used for diluting the partially desorbed acidused for the selective extraction of propylene from the residual gases.

In order to describe the invention in more detail, reference will now be made to the accompanying drawing illustrating a diagram' of ilow suitable for the'manufacture of gasoline;

As indicated in the drawing, a cracked naphtha distillate is conducted from a source not shown through a pipe l. This distillate may be obtained that two or more fractionating towers may be employed, the single tower indicated being merely diagrammatic.

The Cliraction is passed through a pipe 3 to lan alkylation unit 4, shown in broken lines.

This unit may comprise a plurality of apparatus including reaction vessels, separating vessels and fractional-.ing equipment.

In the alkylation operation the C4 fraction conalkylation of the aromatic hydrocarbon with 65 taining oletlns is reacted with isobutane in the While a such as ethyl benzene.

vpresence of concentrated sulphuric acid. The

isobutane is conducted from a source not shown through a pipe S while the acid is also conducted from a source not shown through a pipe 8.

The acid as already indicated has a concentration of about 94 to 100% H1304 on the basis of freedom from organic material.

The method of carrying out the alkylation reaction with concentrated sulphuric acid is now well known in the art andtherefore need not be described in detail. The alkylated hydrocarbons may comprise some hydrocarbons boiling above the range of gasoline and 4therefore the alkylation unit may comprise provision for fractionating the A alkylated gasoline hydrocarbons from the undesired higher boiling material.

At any rate the alkylated gasoline hydrocarbons are discharged from the unit through a pipe 1 while spent acid of about 90% H2804 (organic free) is discharged from the unit through a pipe l.

Referring again to the stabilizer 2, the Ca and lighter fraction is removed through a pipe III which leads to the lower portion of a primary extraction tower I2. The C; and lighter hydrocarbons rise through the tower countercurrently to a streamof partially desorbed acid or diluted acid as will hereinafter be described. The extraction in the tower I2 is carried out under a temperature in the range of about 60 to 100 vF. and under a pressure ranging from about 2 to 110 atmospheres. Propylene is absorbed' in the acid and continuously discharged from the bottom of the tower through a pipe I2.

The residual gas containing ethylene and saturated parailln hydrocarbons is continuously removed from the top of the tower through a pipe I4 which leads to the lower portion of a secondary extraction tower I5. In this extraction tower the gases rise countercurrently to a stream of spent alkylation acid, being introduced to the upper portion of the tower through the pipe 8. This extraction is carried out under a temperature ranging from about 50 to 175 F. and preferably from about 90 to 125' F. The pressure will range from about 1 to 100 atmospheres. Conditions are thus maintained so that ethylene is ex tracted by the spent acid. The resulting ethyleneacid mixture is discharged froml the bottom of the tower through a pipe I6 while the residualI gases are discharged through the pipe I1.

The ethylene acid mixture will comprise ethylene in the form of ethyl disulphate and ethylene hydrogen sulphate. This mixture is passed to a desorption unit wherein the acid mixture isy subject to an elevated temperature in the range 350 to about 500 F. y The heating is carried out so that the acid mixture is exposed to the elevated temperature for a short period of time insumcient to cause substantial decomposition.

The desorption is carried out so as to liberate about 50 to 60% of the'ethylene in pure form whichis discharged through pipe 2l.

lallorinpaxtis Pipe I3 a,sos,sos p tower l2 so that the residual ethylene contained in the acid is displaced therefrom by the propylene contained in the feed gas entering the tower. The displaced ethylene passes overhead through the pipe Il. Thus. the propylene acid mixture drawn oi! from the tower through the is substantially free from ethylene. Y The propylene acid mixture drawn oi! through the pipe Il may be conducted in part through a branch pipe 3l leading to a hydrolysis unit II, shown in broken lines, wherein the propylene sulphate is converted to alcohol. Spent acid is drawn off fromthe hydrolysis unit through a pipe 22.

On the other hand, the propylene acid mixture conducted through a branch pipe 2l leading to an amlation unit 26, shownin broken lines. v' Y An aromatic hydrocarbon auch as benzene, or a mixture of aromatica, is conducted through a pipe 21 to the alkylation unit. Free sulphuric acid or about 85% concentration may be introduced from a pipe 3| to the alkylation unit Il. Conditions are maintained in the alkylation unit .so that the benzene reacts with the propyl ester to produce alkylated aromatic hydrocarbons comprising mainly cumene. The alkylation reaction may be carried out at a temperature in the range of about 'l5 to 175 F. The amount of free sulphuric acid added through the pipe 28 may amount to about 1 to 2 parts by weight of the propylene acid mixture entering the alkylation unit. y

As in the case of the aliphatic alkylation unit I the aromatic alkylation unit, may comprise a plurality of apparatus including provision for fractionating undesired high boiling material from the alkylate. The alkylated aromatics are removed through a pipe 29.

'I'he spent acid from drawn of! through al pipe 40 and conducted all or in part to an acid concentrating unit 4I of conventional design andy operation. The concentration of the acid is thus brought up to the range of about 94 to 100% which is effective as a catalyst for the aliphatic alkylation unit.

As indicated, some of the spent acid from the alkylation unit 36 may be by-passed through a branch pipe I3 which communicates with the pipe 22. The purpose of this is to adjust the l concentration of the acid used in the extraction The ethylene so liberated is sufficiently pure to be useful for the manufacture of chemicals in theforxn of ethyl theprimary extractlngmedium therein. Conditions are maintained in the extraction 75 450 concentration so that it is' tower I2 whenver this may be necessary.

Thus, the concentration of sulphuric acid effective for the absorption of propylene is usually in the range of about l5 to 85% basis organic free. It is contemplated, however, that the ethylene hydrogen sulphate mixture passing through the pipe 22 will he adequate without further adjustment 'of the acid yconcentration to effect the seiected extraction of propylene from the feed gases entering the tower l2.

The spent acid drawn on from the hydrolysis unit the pipe 22 may also he passed via pe l! to the acid concentration unit Il.

-The aromatic hydrocarbon or hydrocarbons used in the alkylation unit 38 may be derived from the stabilized naphtha by extraction with a suitable solvent.

For example. the stabilized naphtha removed from thestabiiiacr 2 through a pipe 50 may be the alkylation unit 36 is assasoc sumcient to maintain liquid phase conditions. In this way the aromatic hydrocarbons are preierentially dissolved in the water and the water The non-aromatic portion of the naphtha is removed through a pipe 54 which may communicate b with a pipe 55 leading to a blending tank 56.

The pipe 55 also communicates with the pipe 50 to permit passing stabilized naphtha tothe tank 56.

Likewise, the pipe 1 communicates with the tank 56 to permit passing alkylated gasoline thereto.

The aromatic alkylate discharged through the pipe 39 may also pass to the blending tank 58. The several hydrocarbon components are thus blended to produce ahigh quality gasoline product.

As indicated'in the drawing, provision 'may be made for fractionating the aliphatic alkylate and the aromatic alkylate outside their respective alkylation units. Thus. these two alkylated products may be discharged through a pipe 60 leading to a fractionator 6| wherein they are fractionated in the presence of each other to produce a distillate fractionwhich may be recycled through a pipe 62 to the blending tank 58.

Obviously many modiications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim: i

1. A continuous method of selectively separating propylene and ethylene from a normally gaseous mixture of hydrocarbons which Acomprises passing a stream of said gaseous mixture through aprimary extraction zone, subjecting it therein to contact with an extraction medium comprising partially desorbed sulphuric acid from a source later referred to, effecting said contact under conditions such that propylene is extracted by the partially desorbed sulphuric acid from a source later referred to. eecting said contact under conditions such that propylene is extracted by the acid from ethylene and non-oleilnic hydrocarbons Iin said gaseous mixture, separatelyremoving residual ethylene gas and propylene rich acid, passing said residual gas through a secondary extraction zone, subjecting it therein to contact with sulphuric acid ofA about 90 to 94% organic free acidity. effecting said contact in the secondary zone under conditions such that ethylene is extracted by the acid from the residual gas, separately discharging the residual gas and ethylene rich acid, subjecting the ethylene rich acid to elevated temperature whereby a major portion of the ethylene is liberated to produce partially desorbed acid, discharging the liberated ethylene, passing partially desorbed acid to the primary extraction zone as the .said extraction medium, treating said propylene rich acid to effect removal of propylene and produce spent acid, and passing at least a portion of said spent acid to said primary extraction zone. v

3. A process for gasoline manufacture from C4 and lighter hydrocarbons containing oleiins which comprises forming a C4 fraction and a C3 and lighter fraction, subjecting said C4 Ifraction to alkylation with a'low boiling isoparafiln in the presence of `concentrated sulphuric acid in an aliphatic alkylation zone, removing from said zone alkylated gasoline and spent alkylation acid, subjecting said C3 and lighter fraction to contact in a primary extraction zone with an extraction medium comprising partially desorbed sulphuric acid, eiecting said contact under conditions such that propylene is extracted by the acid from ethylene and non-oleflnic hydrocarbons in said Ca and lighter fraction, removing from the primary extraction zone residual ethylene gas and propylene rich acid, passing said residual gas through a secondary extraction zone, subjecting it therein to acid from ethylene andnon-oleiinic hydrocarbons in said gaseous mixture, separately removing residual ethylene gas and propylene rich acid, passing said residual gas through a secondary extraction zone, subjecting it therein to contact with sulphuric acid of about 90 to 94% organic free acidity, eecting said contact in the secondary zone-under conditions such that ethylene is extracted by the acid from the residual gas, separately discharging the residual gas and ethylene rich acid, subjecting the ethylene rich acid to elevated temperature whereby a major portion of the ethylene is liberated to produce partially desorbed acid, discharging the liberated ethylene and passing said partially desorbed acid to the primary extraction zone as the said extraction medium.

2. A continuous method of selectively separating propylene and ethylene from a normally gaseous mixture of hydrocarbons which comprises passing a stream oi' said gaseous mixture through a primary extraction zone, subjecting it therein to contact with an extraction medium comprising contact with said spent alkylation acid, effecting said contact under conditions such that ethylene is extracted by the acid from the residual gas, separately discharging residual gas and ethylene rich acid i'rom the secondary extraction zone, sub- Jecting the ethylene rich acid to elevated temperature whereby a major portion of the ethylene isv liberated to produce partially desorbed acid, discharging liberated ethylene, recycling said partially desorbed acid to the primary extraction zone, liberating spent acid from the propylene 'rich acid mixture, reconcentrating said liberated acid and recycling the reconcentrated acid to the aliphatic alkylation zone.

4. A process for gasoline manufacture from C4 and lighter hydrocarbons containing oleflns which ene land non-oleiinic hydrocarbons in said Ca and lighter fraction, removing from the primary exl traction zone residual ethylene gas and propylene rich acid, passing said residual gas through a secondary extraction zone, subjecting it therein to contact with said spent alkylation,acid,'eifect ing said contact under conditions such that ethyl-

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