US2334955A - Alkylation process employing evaporative cooling - Google Patents

Description

Nov. 2,334,955

ALKYLATION PRocEss EMPLOYING EvAPoRATIvE COOLING 23, 1943- vD. H. PUTNEY Filed March 14, 1942 f INVEN TOR.

05W/d /7 paf/@QJ m ESM www K mkg @MW S Patented Nov. 23, 1943 ALKYLATION PROCESS EMPLOYING EVAPOBATIVE COOLING David H. Putney,

Kamm city, Mo., mimmto Stratford Development Corporation, Kansas City, Mo.,

a corporation of Delaware Application March 14, 1942, Serial No. 434,855 3 Claims. 28B-883.4)

This invention relates to improvements in an alkylation process employing evaporative cooling and refers more particularly to a method for vapplying direct evaporative refrigeration to the acid and hydrocarbon enluent discharged from an alkylation reaction, for the purpose of buildy ing up the iso-butane-oleiin ratio in the reaction zone and eliminatingall heat transfer surfaces from the reaction zone.'v

It has been found that, by passing the hydrocarbon and acid eiiluent from an alkylation reaction zone intoy a flash zone operated at reduced pressure, a portion of the volatile hydrocarbon components can be evaporated and the heat of vaporization being supplied by a drop in temperature of the acid and remaining hydrocarbon to such an extent that' the reduced iemperature of the acid which is then returned to the reaction zone, will carry the entire refrigeration load required to operate the alkylation reaction at optimum temperatures. The vapors separated during the evaporation are rich in isobutane, due to the high iso-butane content of the hydrocarbon eiiiuent. The condensate recovered from thesel vapors can be recycled as a part of the charge to the alkylation reaction stage for building up the concentration of isobutane in the feed in the same manner as the iso-butane recycle recovered from fractionation of the alkylate is used to accomplish the same result. Thisis particularly true when alkylating feed stocks which result in a low concentration of normal butane in the eiiiuent.

Other so-called autorefrigerated or evapora- 4 tive cooling systems have been developed for alkylation processes and some are at the present time being utilized in commercial plants. In these, however, the volatile hydrocarbon components are directly evaporated from the alklation zone. The refrigerant therefore does not exist as a liquid in the eiiiuent discharged from the reaction zone but is removed as a vapor from I the reaction as fast as it is introduced. Condensed refrigerant recovered from the evaporated materials therefore does not increase the iso-butane-oleiin ratio in the reaction zone.

As distinguished from thisgtype of evaporative cooling. the present method proposes to take full advantage of the iso-butane refrigerant during its passage through the reaction and catalyst-settling stages as it exerts in both stages an influencing factor favorable to the production of iso-octane in the reaction zone and as a fluid medium advantageous to more complete settling in the acid settler.

I4 by means of 4 Another advantage of the present method is the elimination of all heat transfer surfaces from the reaction circuit, thus making for simplicity and reduction or' equipment cost particularly in cases of large installations where multiple reactors and multiple tube bundles would otherwise have to be employed. f;

Further advantages of the process will appear from the specification.

The singlengure, which forms part of the specification and isV to be `read .in conjunction therewith, is a `schematic ilow diagram of an apparatus adapted to the operation of the process. l f

For purposes of illustration but not by way of limitation and for convenience in phraseology, we will refer to the iso-paradinic hydrocarbon as iso-butane and we will refer to the oleilnic hydrocarbon as butylene, it being understood that any of the iso-paralnic hydrocarbons may be alkylated by means of any of the oleilnic' hydrocarbona.

Referring to the drawing and describing the process in connection therewith, a normally gaseous feed stock having a of oleilnic'hydrocarbons is charged from any convenient source through the pipe i and is mixed in pipe 2 with a second [normally gaseous feed stock containing iso-paraillnic C4 hydrocarbons supplied through pipe 3., -This mixture in liquid phase is accumulated inf'a feed tank 4 from which it is withdrawn through pipe i and charged by means of pump t through line l in which is interposed a heat exchanger I and a flow control valve 9. A iluid medium, such as the cold hydrocarbon eiiiuent leaving the system, is circulated invheat exchange relationwith the feed in the'exchanged 8 to bring it to a proper temperature for alkylation in the contactor i0.

A condensation catalyst, such as sulfuric acid, hydroiiuoric acid, phosphoric acid, aluminum chloride, or other catalysts which promote the alkylation reaction, is introduced through pipe ii. In the description of the process and apparatus, for convenience and in the interest oi' simplifying the specication,v the catalyst will be specified as sulfuric acid, but it is contemplated that hydroiluoric acid or any of the other catalysts suggested may be used.

In the contactor is a cylindrical. baille Ila shown in dotted lines, in the lower, open ended, constricted throat of which is positioned aprojl and driven drive, diagrammatically shown at a motor Il. By this mechanism substantial content throughl a gear an intimate mixture of the'paralnic and clefinic hydrocarbons with the condensation catalyst is effected in the contactor by rapid circulation of the constituents upwardly through the passageway formed by the cylindrical baille Illa within the contactor I8.

The character of the feed stock, the catalyst used, the iso-butane-olefin ratio, and the acid concentration form no part of the present invention except that these factors should be regulated to obtain optimum conditions for alkylation in the contacting stage.

To maintain the temperature of reaction within a proper range is the function of the evaporative cooling contemplated by the instant method. The mixture of reacted hydrocarbons and catalyst forming the eilluent from the reaction vzone or contactor I is discharged through pipe I6 and the catalyst separated from the lighter hydrocarbon constituents in the ac id settler I1. To the acid settler, fresh catalyst is supplied through pipe I8 controlled by a valve I9. Acid settledfrom the mixture is withdrawn through pipe 20. Spent acid in an amount equal to the fresh acid feed may be continuously or periodivalve 22. That narinalacid recycle demanded for good` operationele chargedgbypieans of pump 23, lines 24 and 25, to .a flash tower 26. Between pipes 28 and 24 is a pipe 21 controlled by a valve 28 which bypasses the pump 23. Valve 29 in line 24 and valve 38 in line 20 control the flowof acid through'their respective lines. Since the flash tower is normallyv operated at a pressure lower than the pressure on the acid settler I1, the pump 23 will be bypassed .through line 21. A flow control valve 3l in line 24 serves to regulate the amount of catalyst supplied to the flash tower. The lighter hydrocarbon materials sepa-A.

cascades down over a series of trays and is accumulated in the bottom of the tower where there is maintained a lower acid level by the liquid level control device 39, and an upper liquid level of hydrocarbon materials by means of liquid level control device 48. The heavier acid is withdrawn from the bottom of the tower through pipe 4I and is recycled by pump 42 through pipe II, the valve which controls liquid level 39 being interposed in this latter line. The unevaporated alkylate containing hydrocarbon mixture is withdrawn from the tower 26 4through pipe 43 and is discharged by pump 44 through line 46 to the final settler 46. In the pipe 46 is interposed a control valve which is regulated by the liquid control device 48. Any entrained liquid catalyst, separated in the final settler 46, is returned through pipe 41 to pipe 4I for recycling to the alkylation stage.

As explained, in the flash tower 26 there is maintained a lower acid level and an upper hydrocarbon level. Since the base of the flash tower is not an ideal settler, it is proposed to take the hydrocarbon alkylate from the flash tower through thenal settler 46 for the purpose of a1- the neutralization and fractionation equipment:

The small amount of acid settled out in the final settler 46 can be either continuously or periodically passed to the acid pump 42 and returned to the contactor. It does not matter if some hydrocarbon is entrained in the acid being returned to the contactor from the base of the flash tower or from finalsettler-46.

The alkylate containing hydrocarbon mixture separated in the nal settler 46 is passed through line 48, through a heat exchanger 48 which may be identical to exchanger 8 as previously suggested, and pipe 60 to neutralization and fractionation equipment diagrammatically shown by the rectangular block 6I.

This equipment normally will include the conventional soda mixing, settling equipment and fractionation equipment, such as a depropanlzer, a de-isobutanizer, stabilizer, and rerun towers. Iso-butane recovered from fractionating equipment, is recycled through pipe 62 to the feed tank 4. Normal butane is diverted from the system through pipe 63 controlled by valve 64. C: fractions and lighter are diverted through pipe 66 controlled by valve 66. Materials within the alkylate range are recovered through pipe'61, regulated by valve 68, and the bottoms from the alkylate rerun tower are taken oil. through pipe 69, controlled by valve 60.

It is inadvisable to pass the mixture of hydrocarbon and acid eiiluent from the contactor Il direct to the flash tower 26 for the reason that the mixture leaving the contactor is in the form of a hydrocarbon in acid emulsion. A reduction of pressure on such an emulsion would cause boiling and foaming of the acid and possibly result in acid foam carrying over to the compressor 34. This emulsion is therefore passed first to an acid settler I1 where it is settledinto a clear hydrocarbon and a flatv acid. 'I'hese two streams are passed to the flash tower through pipes 32 and 24 where they comein contact with each other but are not mixed to the extent that an emulsion is formed. The flash tower can thus be operated Without foaming and the hydrocarbon and acid can be readily separated after being chilled.

The necessity of making a separation of the acid and hydrocarbons as in the settler I1 between the reactor I8 and flash tower 26 depends largely upon the degree of mixing or emulsiflcation in the reactor. In some cases the mixture leaving the reactor may be of such nature as to permit its introduction directly to the flash tower 26 without separation. If the settler I1 is eliminated the fresh acid feed could be supplied either to the flash tower 26 or contactor I0 and the spent acid removed from line 4I.

The contactor, acid settler and final settler are operated liquid-full, under' pressure. 'Ihe flash tower is operated at reduced pressure andV in the case of C4 'alkylatiom at from 8 to 15 pounds absolute.

As an example, when this method is used to alkylate a C4 feed stock having between 16 and 20% normal butane in the eilluent from the contactor I0, the following conditions may exist:

Reaction temperature of 50 F.; per cent acid in the mix, 60%; temperature of the acid returned to the contactor, 13 F. to 15 F.; pressure on the flash tower, 10-to l2 pounds per square inch absolute; external ratio iso-butane to olen built up by fractionation, ranging between 3.0/1 to 3.5/1; external ratio of feed stock including compressor condensate 11/1; iso-butane content of eiiiuent 65% to 75%.

An inspection of the above conditions shows them to be proper for the production of the exceptionally high quality alkylate and depending upon the nature of the C4 olens the alkylate would be expected to contain a raw aviation fraction of between 94 to 96 octane by A. S. T. M.- C. F. R. method. Such high quality alkylate could not normally be made from a feed stock having an external ratio of only 3.0/1 to 3.5/1. It is only by virtue of the compressor condensate being returned to the feed that the ratio is raised to approximately 11/1 and the quality thus improved. Furthermore, the existence of the parafiinic hydrocarbons in liquid form, both in the reaction and settling stages as contrasted with evaporative cooling methods which exhaust these materials from the reaction stage has a very decided advantageous effect upon the character of the :Final alkylate produced.

It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and ls within the scope of my claims. It is further obvious that various changes may be made in ietails Within the scope of my claims without departing from the spirit of my invention. It is, ;herefore, to be understood that my invention snot to be limited to the specific details shown md described.

Having thus described my invention, I claim:

1. A method of alkylating iso-parafllnic hydro- :arbons' with olenic hydrocarbons comprising zhe steps of intimately contacting the iso-parafnic and olenic hydrocarbons in a reaction step n the presence of a condensation catalyst at a oredetermined temperature, withdrawing the reicted products and catalyst from the reaction atep and passing them to an intermediate sepalating step under pressure suillcient to maintain ,hem in liquid phase and there separating the :atalyst from the hydrocarbons, separately introlucing said catalyst and hydrocarbons into a reluced pressure zone at points spaced far enough spart to prevent the formation of an emulsion ind foaming. vaporizing a portion of said hylrocarbons by the reduction in pressure and hereby cooling the catalyst, returning the cooled atalyst to the reaction step, and controlling the emperature and quantity of said recycled catalyst as a function of the required temperature in the reaction step.

2. A method oi' alkvlating iso-paraiilnic hydrocarbons with oleflnic hydrocarbons comprising the steps of intimately contacting the isoparaflinic and oleiinic hydrocarbons in a reaction step in the presence of a condensation catalyst at a predetermined temperature, withdrawing the reacted products and catalyst from the reaction step and passing them to an intermediate separating step under pressure suilicient to maintain them in liquid phase, and there separating the catalyst from the hydrocarbons, separately introducing said catalyst and hydrocarbons into a reduced pressure zone at points spaced far enough apart to prevent the formation of an emulsion and foaming, vaporizing a portion of said hydrocarbons by the reduction in pressure and thereby cooling the catalyst, recycling the vaporized hydrocarbons to the reaction step as a constituent of the feed thereto, returning separately the cooled catalyst to the reaction step, and controlling the temperature and quantity of said recycled catalyst as a function ofthe required temperature in the reaction step.

3. A method of alkylating iso-paraflinic hydrocarbons with olefmic hydrocarbons comprising the steps of intimately contacting the iso-parafnic and oleiinic hydrocarbons in a reaction step in the presence of a condensation catalyst at a predetermined temperature, withdrawing the reacted products and catalyst from the reaction step and passing them to an intermediate separating step under pressure suiicient to maintain them in liquid phase, and there separating the catalyst from the hydrocarbons, separately introducing said catalyst and hydrocarbons into a reduced pressure zone at points spaced far enough apart to prevent the formation of an emulsion and foaming, vaporizing a portion of said hydrocarbons by the reduction in pressure and thereby cooling the catalyst, recycling the vaporized hydrocarbons to the reaction step as a constituentl of the feed' thereto, returning separately the cooled catalyst to the reaction step, controlling the temperature and quantity of said recycled catalyst as a function of the required temperature in the reaction step, supplying fresh catalyst to the system, and removing spent catalyst in corresponding amounts to maintain a re1- atively constant concentration of catalyst in the reaction step.

DAVID H. PUTNEY.

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