US2396683A - Production of alkylbenzene - Google Patents

Description

March 19, 1946. .Q R, CARMODY ETAL y 2,396,683

PRODUCTION OF' ALKYLBENZENE Filed Feb. 26. 1943 larly under Patented Mar. 19j, 1946 F CE fran-r PRODUCTION or manzana Don R. Carmody, Hammond, Ind., :and Harold E; Huber, Chicago, Ill., assignors to Standard Oil Company, Indiana Chicago, Iii., a corporation ai Application February 2.6, 19%, Seriali No. 77,224 iii Claims. (Ci. 26d-67d) This invention relates to the production of alkyl aromatic hydrocarbons and relates more particularly to the production of monoalkyl benzene by the alkylation of benzene from a dilute benzene stream with propylene.

Monoalkyl benzenes and particularly the lower boiling monoalkyl benzenes such as butylbenzene and isopropylbenzene (cumene) have been found to be valuable constituents of aviation fuels because of their very high octane number, particusupercharged amount of monalkyl benzenes present in ordinary refinery streams of petroleum hydrocarbons is comparatively negligible and even in the products from such processes as catalytic or thermal cracking, catalytic aromatization and the like, the ultimate yield of low boiling alkyl benzene aroconditions. The

matics is comparatively low. Higher boiling aromatics, such as xylene, are obtained in much higher yield by thermal cracking, catalytic crack'i ing, or hydroforming. However, the paraiiins Y contained in such fractions have relatively low It has been known for some time that these' desirable alkyl benzenes can be synthesized by the alkylation of benzene with oleflns in the presence ofsuitable catalysts. The above processes give rise to some benzene but the actual volume is lowand the benzene is present only in low concentrations. Concentration of all ofthe dilute benzene by various means such as byazeotropic distillation, fractional condensation, solvent extraction, adsorption, and the like has not been practicable. Consequently dilute benzene has not been an economical source of benzene for alkylation which heretofore has required concentrated benzene derived from coal tars, for example. timum cleanup of benzene from dilute benzene streams by simply alkylating to yform the desired monoalkylbenzenes, however, is'not the solution since the recycling of the unreacted benzene to the alkylation is not feasible because of the inert diluent.

It is an object of this invention tovprovide an improved process for the economical alkylation of an aromatic from an. aromatic-containing dilute stream with oleinic hydrocarbons. Another object of our invention is to provide an improved process for the production of monoalkyl benzenes from dilute benzene-containing streams wherein the necessity for concentrating the benzene is reduced to a minimum. A still further object oi our invention is to provide an integrated process wherein hydrocarbons valuable for aviation fuels are prepared from a dilute benzene stream by a combination of steps. Further objects and advantages will become apparent as the description of our invention proceeds.

Briey stated our invention contemplates a unitary process including the aikylation of a) dilute benzene hydrocarbon stream with an excess oi' olens by contacting in the presence of an alkylation catalyst at temperatures within the range of between about 400 and about 600 F. When propylene is the olen the benzene is alkylated from the stream to produce cumene and polyisopropylbenzcne. Another step in our unitary process is subjecting the alkylate comprising polyalkylbenzenes toy disproportionation in the presence of added benzene and the alkylation catalyst, such as solid phosphoric acid, at a higher temperature above about 450 F. within the range of between about 500 and 700 F. to produce additional monoalkyl benzenes by a dealkylationalkylation. A recycle benzene fraction anda polyalisyl benzene fraction can be returned to the disproportinatlon to form additional monoalkyl benrzenes.v When the benzene'content of the recycle benzene from the disproportionation step becomes diluted it may be recycled to the dilute benzene alkylation step to produce additional .polyalkyl vbenzenes.

When operating with dilute benzene it is necessary to employ propylene-benzene mol ratios` higher than one in order to remove most of the benzene. Onlyby using excess olens can the benzene cleanup exceed about 50%. When 50% of the total benzene is alkylated approximately 75% of the alkylate is cumene and 25% is polysopropylbenzene. By increasing the propylenebenzene mol ratio, the benzene cleanup can be increased to 75% under which conditions the alkylate contains about equal amountsv of cumene and polyisopropylbenzena Thus'the use of a molar excess of olelns to effect high benzene cleanup from dilute streams produces higher boiling polyalkylbenzenes unsuitable for use as motor or aviation fuel.` The latter productcan be disproportionated with concentrated benzene at somewhat higher temperatures, i. e. about 500 F. as compared with 450 F. for alkylation, both for example in the presence of phosphoric acid catalyst; Y

illustrates apparatus suitable for carrying out one .preferred embodiment of our invention and it is in the form of a simplied flow diagram.

Referring to they drawing a dilute benzenek stream, such as that derived from naphthas and.

The accompanying drawing diagrammatically` about ve or higher, for example above about 2.5. The combined charge is fed at the rate of between 0.01 to 1.0, for example below about 0.3 gallon per hour per pound of catalystwithin the reactor for` maximum olefin and benzene cleanup. `Re action pressure affects the olen and benzene cleanup and a pressureof between about 50 and about 300 P, S. I. is contemplated.

tion a benzene cutwhaving 60`to 100% benzene vand to recycle the unreacted benzene fraction A- until the concentration becomes uneconomical at which time it can be recycled to the alkylation zone I to be converted to monoand polyalkyl-v benzenes-Which are subsequently disproportionated in the disproportionator I8 or withdrawn,

- concentrated, and returned via line l1.

The alkylator I0 can be any conventional reactor for contacting hydrocarbons and catalyst and suitably can be a Atower containing a bed of stipported catalyst, for example phosphoric acid on kieselguhr. Other forms of catalytic contacting apparatus such as so-called fluid catalyst systems wherein the catalyst is maintained in a highly dispersed phase or in a dense, turbulent.,

uent phase may be used. Thetemperature Within the alkylator I0 is maintained within the range of between about 400 and about 600 F., for example 450 F. If desired 0.5 to about 2% of feed can comprise an alcohol, which may correspond to the alkylating olen, to maintain the proper degree of hydration in the phosphoric acid catalyst, and to supply part'of the olens.

The alkylation product is withdrawn from a1- `kvlator I0 by line I3 and introduced into fraccan be subjected to a catalytic conversion wherein the inert diluent is removed and the more concentrated benzene is recycled to the alkylation.

Suitable catalysts are hydroforming and solid cracking catalyst. Ifgiesired the catalytic conversion can comprisethe source of the dilute benzene stream, i. e. a hydroforming or catalytic aromatizing' of naphtha. Thus the inert diluent and residualbenzeiie is recycled to the source which may suitably be hydroforming. Merely recycling the diluent and unreacted benzene to the alkylation would only further dilute the.

stream.

The predominantly polyalkylbenzene' cut or a fraction thereof in line I6 is then contacted in the presence of an alkylation catalyst, such as a supported phosphoric acid catalyst, with concentrated benzene introduced into the disproportionation reactor I8, for example, by line I1 and recycled by lines 22 and 25. Concentrated benzene sumcient for the disproportionaton can be recovered from a portion of the dilute benzene alkylation feed` withdrawn for example by line 23. Any desired means of concentration can be used as, for example, an az'eotropic distillation. When lnecessary a portion of the recycle benzene can be bled into the concentrator to remove dil.-

v uents which might accumulate.

It is contemplated that the alkylator I0 and the disproportionator I8 can be used alternately for alkylation and disproportionation by providing the necessary conduits and valves. Thus one can be used at "a lower temperature with fresh catalyst to eectialkylation and then used at the higher temperature for ,disproportionation Two or more reactors can be used in stages, series or parallel.

The examples Aset forth in the following Table I illustrate the importance of the use of the prop-A er molratio of the reactants and low feed rates in the alkylation. In each of the runs the catalyst was phosphoric acid o n kieselguhr.

Table I Example 'sie ressure M01 ratio CrHu/CaHe. Rate gaL/h Product analysis volume per cent: Benzene cutl Isopropylbenzene cut Po yisopropylbenzene cut.. Benzene reacted weight per cent.= Isopkro ylbenzene, per cent ol total a y ate From the above Table I it is apparent that by using a mol ratio of propylene. to benzene less than one the benzene cleanup is insuiilcent to establish an economical process since it is notl feasible to recycle the unreacted benzene plus tThe temperature within the disproportionation zone is maintained within the range of between about 500 F. and about 700 F., for example, at about 650 F. The disproportionation product is withdrawn by-line i9 and introduced into prod uct fractionator 20. The desired monoalkylbenz ene cut is withdrawn from fractionator 20 by line 2|. A benzene overhead cut ordinarily is recycled by line 22 either to the dlsproportionation reactor I8 or to alkylator l0.. An unreacted polyalkylbenzene fraction is withdrawn by line 28 and recycled to the disproportionator I8 by line I6. It is possible to use in the disproportiona-` zene Product analysis. volume per cent: e

tion is converted to the monoalkylbenzenes byl disproportionation over solid phosphoric acid at a temperature in excess of 450 F. The data setA forth in the following Table II indicates the importance of temperature in the disproportionation.

Table I1 Example m rature ..F-. 440 555 Te pe gag.. 230 250 Pressure Rate .gaL/hrJl 0.12 0.08 Feed, weight percent:

t-Butyl alcohol n geiligemi o ro y enz Mol ratio llfolpolyisopropylbent. as'

e sa..

e aan s aa... aaa e aan.

Y alkylbenzenes.

afaoaoea From the above it is apparent that the reaction at 450 F. and below is negligible. but even at these low temperatures the reaction is greater with lower feed rates. At 550 F. the production of monoalkylates is appreciable. At 660 F. the reaction proceeds smoothly. The effect oi pressure is illustrated in Examples 6 and 8 from which it is apparent that at the lower pressures the yield of monoalkylate is perhaps slightly reduced, but not to any appreciable extent..

A disproportionation similar to that illustrated in Table Il does not result when the substituent alkyl group has but one carbon atom to the molecule. Xylenes from which all toluene wasv carefully removed was diluted with an' equal volume of benzene and passed over phosphoric acid catalyst under pressure of 250 P. S. l. for 3.3 hours at a rate of 0.10 gal./hr./lb. at both 550 F. and 650 F. Careful fractionation of the liquid products gave no trace of toluene in eithercase.

By our process large quantities of a very desirable product are produced from a, material heretofore considered wholly unsatisfactory for. 'the purpose.

The necessity ofv concentrating large quantities oi' dilute benzene is avoided and the only benzene which need be concentrated is that used in the disproportionation 'of the poly- By controlling the mol ratio of the olefin to benzene in the alkylation step, an optimum amount of monoand polyalkylbenzenes is produced; The disproportionation oi' these polyalkylbensenes with concentrated benzene is eiiected at low feed rates and in the presence of a catalyst of the same composition as the all-:ylation catalyst. but at a higher temperature.

n one embodiment of our invention, the residual benzene' and inert diluent recovered from the alkylation step is recycled to the catalytic conversion step which provides the dilute benzene stream.

From the foregoing it will be apparent that we have attained the objectsl of our invention and have provided a new process for the production oi monalkylbenzenes from dilute benzene by a combination oi integrated steps.

Although we have described our-process.l with special reference to one embodiment thereof itl should be understood that this is by way of illustration only and not by limitation and that we intend to be limited only to the extent set forth in the appended claims. Moreover various details such as pumps, heat exchangers, automatic control devices and the like have been omitted from the drawing and the description thereof for the sake of simplicity and clarity.

We claim:

l. A process for the production oi isopropylbenzene -'which comprises alkylating a dilute benzene hydrocarbon mixture with oropylene in the presence or" a phosphoric acid alkylation catalyst under alkylation conditions at a temperature below about 450 F.. the mol ratio of propylene to benzene being greater than one, recovering a fraction of the alkylation product having an initial point above about 350 F. and contacting the said fraction with added benzene at a temperature in excess of about 450 F. in the presence of a phosphoric acid alkylation catalyst whereby at least a portion of the added benzene is alkylated.

2. A process for the production ci isopropylbenzene which comprises contacting dilute benzene and propylene under alkylating conditions in the presence of a phosphoric acid catalyst, the

ratio of propylene tobenzene being about three to one..thereby converting a substantial fraction oi the benzene to isopropylbenzene and polyisopropylbenzene, disproportionating the polyisopropylbenzene to isopropylbenzene by contacting with added benzene in the presence of a phosphoric acid catalyst at a temperature substan. tially above that maintained in the alkylation, and at a feed rate of about 0.01 to 1.0 gal./hr./lb. of catalyst. v

. 3. A process for the production of isopropylbenzene which comprises contacting propylene and a dilute benzene hydrocarbon mixture in the presence of an alkylation catalyst under alkylation conditions at-a temperature not in excess of about 450 F., maintaining the mol ratio of. propylene to benzene greater than one, subjecting 'benzene to alkylation in the presence of phosphoric acid therebyproducing an alkylate comprising a mixture of mono and polyalkylbenzenes, subjecting the polyalkylate to disproportionation in the presence of phosphoric acid and added benzene under conditions of temperature and pressure more severe than employed in the alkylation, recovering a recycle benzene fraction, a monoalkylbenzene fraction, and a polyalkylbenzene fraction from said disproportionation, recy` cling the polyalkylbenzene fraction to the said disproportionation and flowing said dilute recycle benzene fraction to the said alkylation.

5. The process for the production of4 monof alkyl aromatic hydrocarbons which comprises cycle benzene fraction, a monoalkylbenzene'fraction and a polyalkylbenzene fraction from said disproportionation, recycling the polyalkylbenzene fraction to the said disproportionation, recycling the benzene to the said disproportionation step so long as the concentration of the benzene therein is in excess of 60%, and iiowing the recycle benzene having a concentration below about 60% tothe said alkylation step wherein the benzene is alkylated to monoand polyalkylbenzenes.

6. The production of a super aviation fuel component by a combination of processes including alkylating a dilute benzene stream with propylene at a temperature at about 450 F. in the presence of a supported phosphoric acid catalyst,

'contacting the polyalkylate with a'second quan-` tity of a supported phosphoric acid catalyst at a temperature above about 450 F. and recovering g from said contacting step a monoalkylate iraction which predominates in isopropylbenzene.

the presence of a solid alkylation catalyst under cess of about 450 F., maintaining the mol ratio of propylene to benzene within the alkylation zone at a value greater than one, recovering a light 'fraction from the alkylation having an end point of about 220 F. and an isopropylbenzen'e cut, and converting the residuaLaikyiation product including polyisopropylbenzene into isopropylbenzene by contactingvthe residual alkylate with added benzene at a temperature in excess of about 450 F. in thepresence of a solid alkylation catalyst of the composition employed in said alkylation.

8. A process for the production of monoalkylaromatic hydrocarbons in the gasoline boiling range which comprises supplying an olefinand a stream of hydrocarbons including aromatics to an alkylation zone in a mol ratio of oleiin to aromatic of at least 1:1, reacting the said olefin and aromatics in the presence of phosphoric acid alkylation catalyst within said zone under aikylation temperature, withdrawing reaction products including polyalkylaromatics from said zone, passing said reaction products together with additional amounts of aromatics over a phosphoric acid catalyst in a mol ratio of aromatic to polyalkylaromatic of greater than 1: 1 in a second contacting zone, maintaining the temperature Within said second vcontacting zone substantially above that maintained in the alkylation zone, whereby substantial proportions of said added aromatic is converted to alkyl aromatic and substantial proportions of said polyalkylaromatic is converted A alkyiation catalyst at a temperature substantially alkylation conditions at a temperature not in ex- 350 F., supplying said polyalkylbenzene along with added benzene to a second contacting zone, maintaining a mol ratio of benzene to alkyl benzene of at least 4: 1 in the feed to said contacting zone, contacting said polyalkylbenzene and added benzene with a phosphoric acid alkylation catalyst at a temperature in excess of 500 F. within said second contacting zone whereby a substantial proportion of the polyalkylbenzene is converted to monoalkylbenzene and a proportion of the' benzene is alkylated to monoalkylbenzene, sep arating the reaction products to recover at least one fraction including benzene and recycling the benzene to the said second contacting step.

10. A process for the production of isopropylbenzene which comprises supplying propylene and benzene diluted with other hydrocarbons to a rst contacting zone, the ratio of propylene to benzene being at least 1: l, reacting the propylene and benzene in said contacting zone in the presence of a phosphoric acid alkylation catalyst to produce a mixture of isopropyibenzene and polyisopropylbenzenes, and contacting the polyisopropylbenzene and added benzene in a second con; tacting zone in the presence of a phosphoric acid above that maintained in the rst contacting zone, the mol ratio of benzene to polyisopropylbenzene feed to the second contacting zone being substantially greater than 1. 1.

11. The process of makingcumene which comprises the steps of alkylating dilute benzene' and a molal excess of propylene in the presence of a solid alkylation catalyst at a temperature between about 400 and 600 F., and disproportionating diisopropylbenzene produced by said aikylation step. disproportionating being effected at a temperature higher than the temperature of the alkyla tion step and within the range of between about 500 and -7 00 F. in the presence of a disproportionation catalyst comprising a solid alkylation catalyst of the' composition employed in the reaction which produced the diisopropylbenzene.

DoinA R. CARMODY. HAROLD E. HUBER.

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