US2730557A - Production of alkyl aromatic hydrocarbons - Google Patents

Description

Jan. 10, 1956 N. MAX ET AL PRODUCTION OF' ALKYL AROMATIC HYDROCARBONS 2 Sheets-Sheet 1 Filed March 2, 1954 Jan. l0, 1956 N. MAX ET AL PRODUCTION OF ALKYI.. AROMATIC HYDROCARBONS Filed March 2, 1954 Saparoor 2 Sheets-Sheet 2 Ypa. Schoofsrna Be: f77- of whichiparadialkyl benzenes Y of the ortho- PRODUCTION GF ALKYL .ARUMATIC HYDROCARRNS? icolaas Max andYp Schaafsma, Amsterdam, Netherland'sya'ssignors to Shell DevelopmentCompany, Eineryvill'e, Calif., .a corporation of Delaware Application March 2, 1954, seminato; traste maints-priority, application Great Britain March .6, `1953/. z'ciaims.' (crezca-71) .This'invention relates to theconversion of hydrocarbons primarily to dialkyl benzenes. Moreparticularly the' invention relates'to acombination of Vprocesssteps by means andfespecially para-diisopropyl'benzene may beproduced ingood` yields with'a minimum loss to productsfof low vail-ue.

In the `refining of petroleum, and more specifically the various cracking' and reforming operations involved in such" refining, considerable amounts kof propylene are formed. It has been the practice to polymerizethis'propylene, either by itselforin conjunction withbutylene, to produce liquid polymerproducts which may be blended with the gasoline eitheras is or after hydrogenation. In the alternative`,the propylene may be used to alkylatearomatichydrocarbons the alkyla'te can be incorporated in the gasoline or other fuelr asa blending component. However, such alkylate consistsof the-various isomers which diler widely in suitability'and as a consequence the mixture has only a nominal Value as a blending component. Thus, for example,4 the para-isomers are generally excellent components'f'havingvery highblending octane numbers and rich mixture ratings whereas the metaand ortho-isomers are comparatively poorcomponents. Also, the paraisomers'iin'd'wider application in other fields such as for instance, jinv `the chemical `iield.

It is found that the desired para-dialkyl benzene may be y produced tothel substantial exclusion of other products by the following described process, the essential feature of which is in `choosing the reactants and conditions and combining the steps in such a manner that continuous operation can be effected without excessive build-up of side vreaction products and consequent requirement of a large bleed stream. In the first place, in order for the process to be economical, it is necessary that the desired product be separable from the gross product by ordinary fractional distillation. This can be readily accomplished in the case ofthe isomers of the poly-substituted isopropyl benzenes provided that interfering products are substantially excluded whereas it is not possible with the methyl and ethyl homologues. Secondly, although it is possible to react propylene with toluene, ethyl benzene, butyl benzene, xylenes, etc., the products generally boil outside of the gasoline boiling range. It is therefore preferred to utilize benzene ora benzene-rich fraction in the process.

. The process of the invention in broad outline comprises the steps of alkylating benzene with propylene to produce a mixture of alkylated benzenes containing substantial amounts of the'isomeric diisopropyl benzenes, fractionating the product to separate a fraction of diisopropyl benzenes and a fraction of heavier alkylated products including triand tetra-isopropyl benzenes, fractionating the isopropyll benzenes to separate a fraction containing most and meta-isomers, and a fraction containing the para-isomer, cracking the fraction containing the orthoand meta-isomers and'also, if desired, part of the heavier products `under special conditions to produce primarily the mono-isopropyl benzene with a minimum of hydrogen such as benzene, toluene, xylene, and the'like, and

2 v transfer reaction whereby the buildup of secondary reaction products in the system is minimized, recycling unconverted products in the cracking step, products to the alkylation step, up of interfering l'products by from the system.

The process will be described in more detail in connection with the description of a typical operation in which description reference may be had tothe ow diagram in Figure I of the accompanying'drawing.

Thel reforming and shown in the ow diagram by-blocks 3 and S are not essential tothe process but are shown to illustrate how the process may be advantageously tied in with renery operations.

Referring to the drawing, line l is fractionated in a conventional topping section 2 into various straight-run products including a straight-run naphtha and a straight-run gas oil fraction. The straightrun naphtha'is reformed in the reforming section 3, e. g.,

and controlling the buildby the conventional platforrning process, to produce a p to a fractionating column 9' wherein itis topped up to a= temperature of about 198-203 C. The overhead frac tion containing unconverted benzene may` be` recycled tot the alkylation 'unit by lineltl; The bottom product fromz fractionating column 9 is passed by line 1'1 to a fractionating column 12in which itis againtoppedto a temperature: C. to produce an overhead fraction. containing' most ofjth'eV orthoand meta-diisopropyl' ben-- The bottom product from `fractionating;

zene isomers. column Ll2is passed by line/13` to a fractionating column 14 inwhich itis again topped to a temperature of abouti 209#215C. to produce as an'overhead; product a frac-- tion of, or consisting'largely of, para-diisopropyl benzene,A andbottom fraction consisting largely.y oftriand tetraisopropyl benzenes.

The overhead product from fractionatingl column 12 is, passed byline 15' to a second catalytic cracking section l5,-

operated under special conditions. If desired, all or part` of the heavier-fraction from line17 may also be passed to` this second catalytic cracking system or, if desired, this. or in whole by line 3.8i to the first catalytic cracking system 5. In the preferredV material may be'returned inV part operation this stream is split'with part going to each: catalytic cracking system for reasons which will be later explained. Also, in some cases, it

catalytic cracking unit 16.V This increases the load on the: catalytic cracking system 16 but allows fractionating columns 9`and 12to be combined into a single column.l

If desired', the liquid product from the catalytic cracking -system 16 may be recycled by line 20 to the alkylation unit '7. However, in order to decrease the volume of material passed to fractionating column I4, and alsov to recoverv small amounts of para-isopropyl benzene produced in the cracking step either by cracking of higher alkylated products or possibly by some small amount of-4 isomerization, it is'desirable to' cycle this product by line 19 tothe fractionating columns 9, 12, and.14. In the alternative this stream may be subjected to separate fractionation and only the-benzene and'mono-alkyl benzeneI cycling the converted.,

a minimum bleed streamv main catalytic cracking systemv crude petroleum entering byv and alkylation catalysts mayy alkylate is passed byline 8:

Y may be desirable to pass: the overheadS fraction from fractionating column 9 to thecharged to the alkylation unit. The gaseous product from the catalytic cracking unit 16 is preferably cycled to the alkylation unit by line 21. In the preferred embodiment the cracking in catalytic cracking unit 16 is carried out in the presence of a diluent such as steam or hydrogen which is advantageously the hydrogen gas produced in the reforming unit 4 and which is introduced by line 22. The hydrogen in the efiiuent from the catalytic cracking unit may be advantageously separated in a system not shown and recycled in the catalytic cracking unit, or the separation may be effected in the alkylation unit itself in which case the alkylation is also carried out in the presence of added hydrogen.

In the system described the operation of the catalytic cracking unit 16 is critical. In normal catalytic crackingT there take place, besides straight cracking, various other important reactions such, for example, as hydrogen transfer, polymerization, and condensation. Hydrogen transfer results in the conversion of unsaturated products to saturated products at the expense of hydrogen taken from material which is converted to the usual tars and so-called coke. This reaction is undesired in the present process since it leads to the build-up of saturated gases in addition to loss of valuable propylene. Polymerization and condensation do not normally occur to a large extent and are, therefore, relatively unimportant as far as the formation of higher boiling products are concerned. They are most important reactions, however, in regard to the present process since higher boiling products of these reactions are generally recracked to produce ethylene and especially large proportions of butylenes. These products, even when produced in only small overall percentages, are quite detrimental in the present process as they alkylate the aromatics in the alkylation step to produce mixed alkyl aromatics and higher boiling products which tend to build up in the system and make the necessary separation by fractional distillation impossible or at least impracticable. it is therefore necessary that the catalytic cracking in unit 16 be carried out in such a way, and under such conditions, that these reactions are minimized. This is preferably accomplished by employing low temperatures in the range of 300-425 C. in the presence of at least 50% by volume of diluent gas and a selective catalyst. it may also be effected, although not as well,

by operating at higher temperatures up to and including f 500 C. provided that the conversion is severely limited by employing only very limited contact times of the order ot 0.1 to l second. Under these conditions only a few per cent at most, e. g., 5% of benzene is found in the cracked products. Thus, for example, when operating at 350 C. with a contact time of 3.5 seconds only 1% benzene was found in the conversion products. At the same temperature but at a contact time of 11 seconds the concentration of benzene in the product was only 2.5%. On the other hand, when operating at 450 C. with a contact time of 3 seconds, the product contained 28% benzene and considerable side reaction products of the kind that interfere in the process. The actual contact time in seconds is difficult to determine accurately. However, it may be fairly estimated by calculating the volume of the total products per second at the reaction temperature and pressure, and dividing this quantity into the volume of the reaction space.

The catalytic cracking in unit 16 may be carried out with any of the conventional cracking catalysts; however, it is found that certain types of catalyst are better than others for the present purpose. Thus, Attapulgus clay and similar clays, supported phosphoric acid catalysts, and treated synthetic silica-alumina cracking catalysts (see below) are especially suited since they catalyze the mentioned undesired side reactions to a lesser degree and, therefore, allow operation with limited recirculation of ethyl and butyl alkylated products with lesser bleeding of the recycled stream. Ordinarily synthetic silicaalumina cracking catalyst, silica-magnesia cracking catalyst, and boric o-xide-alumina cracking catalyst may be used but are inferior to those listed above.

The conventional silica-alumina cracking catalyst is rather unselective but may be made selective by treating it with steam. A suitable steam treatment reduces the available surface to around 350 m.2/g. or below. This treatment may be effected in a separate treatment. On the other hand, the catalyst receives an equivalent treatment during normal use in catalytic cracking. One can therefore use partially spent catalyst from the catalytic cracking unit 5. Thus, fresh catalyst may be added to the catalytic cracking unit 5 by line 23 and partially spent catalyst from this unit may be passed by line 24 to the catalytic cracking unit 16 to supply the needs thereof. This arrangement results in advantages in both units.

In general, the catalytic cracking will be carried out using the catalyst in powdered form. However, other systems using fixed beds or moving beds of catalyst may be used. One suitable arrangement for obtaining the short contact time with powdered catalyst is illustrated in Figure il of the accompanying drawing. In this system the hot catalyst from a catalyst regenerator 30, which may be a separate regenerator or the regenerator of a conventional unit in the catalytic cracking system 5, is withdrawn by a standpipe 31 and is picked up and dispersed by a stream of gas diluent such as steam or preferably the hydrogen gas from line 22 (Figure I), and carried up through a tubular reactor 33 which discharges into a separation vessel 34. The material to be cracked is injected by line 35 into the stream of hot dispersed catalyst at an intermediate point. After a short contact the vapor-s are immediately separated from the catalyst in the separator vessel 34. The product vapors are withdrawn by line 36 while separated catalyst is withdrawn by line 37. The spent catalyst is picked up and dispersed by steam entering via line 38 and carried by line 39 t0 a vessel 40 from which the catalyst is returned to the regenerator.

It will be apparent from the above that, while the alkylation step has been described with respect to the feeds produced, e. g., from the reforming unit 4 and catalytic cracking unit 5, the alkylation actually is much more complicated since it involves alkylation of the quite different products from the catalytic cracking unit 16.

As pointed out above, an important feature of the process described is in the means for minimizing the accumulation of side reaction products (which render difficult or impossible the desired separation of the product by commercial fractional distillation) to such an extent that the otherwise necessarily excessively large bleed stream (which would render the process essentially a once through process with low yields) may be avoided with consequent greatly increased yield and economy. While in the present process the required bleed stream is small, such a bleed stream cannot be dispensed with altogether. ln the preferred embodiment of the process the bleed stream is withdrawn from line 17 by line 13. The amount of material so withdrawn is preferably the minimum consistent with the ability to separate the desired product by commercial fractional distillation, e. g., in fractionating column 14.

The overhead product from fractionating column 14 may be blended with the other usual refinery gasoline components in any desired proportion or combination to produce fuels of the desired characteristics or, if desired, part or all of this product may oe directed to any other use for which it is suited.

Example unit 16 consisting essentially of benzene and cumene was likewise passed to the alkylation unit which resulted in the introduction of 4340 kilograms of cumene to the alkylation unit. The alkylation product (which contained 2085 kilograms of cumene, 1895 kilograms of diisopropyl benzene isomers, 388 kilograms of triisopropyl benzene, 94 kilograms of tetra-isopropyl benzenes, and 106 kilograms of heavy ends) was fractionated at atmos` pheric pressure whereupon 90% (665 kilograms) of the para-diisopropyl benzene was separated as product. The remaining orthoand meta-diisopropyl benzene fraction (1230 kilograms) was passed to a catalytic cracking unit 16 wherein it was cracked at 500 C. with a catalyst consisting of alumina which had been treated with aqueous hydrouoric acid solution to incorporate about 3% fluorine. At a space velocity of 1.7 kilograms per kilogram of catalyst per hour, the conversion was 75%, yielding a converted product containing about 84 mole cumene and lesser amounts of benzene. The unconverted product was recycled to the catalytic cracking step and the converted product was passed to the alkylation step as described.

We claim as our invention:

l. Process for the conversion of hydrocarbons in part to para-dialkyl aromatic hydrocarbons which comprises in combination the steps of catalytically cracking alkylate obtained as hereinafter dened, separating from the products of said cracking a fraction consisting largely of cumene with minor amounts of benzene, passing the said fraction to an alkylation zone wherein it is alkylated with propylene, separating from the resulting alkylate by fractional distillation a fraction consisting largely of paradiisopropyl benzene, passing to the said catalytic cracking a fraction consisting largely of orthoand meta-diisopropyl benzene and catalytcally cracking the same in the presence of at least 50% by volume diluent gas at a temperaperature between 300 C. and 425 C. under conditions whereby very little conversion to benzene, ethylene and butylenes is obtained, passing the cracked product to said alkylation zone as aforesaid, and retaining the concentration of alkyl aromatics having other than C3 alkyl groups Suiciently low in the alkylation product to allow separation of said para-diisopropyl benzene by fractional distillation by withdrawing in addition to and separate from said para-diisopropyl benzene fraction a regulated portion of the alkylate boiling above said para-diisopropyl benzene fraction.

2. Process according to claim l further characterized in that the said catalytic cracking is effected with a cracking catalyst which has been steamed until its surface area is reduced to below 350 square meters per gram.

References Cited in the tile of this patent UNITED STATES PATENTS 2,382,506 Schulze Aug. 14, 1945 2,405,874 Bullard et al Aug. 13, 1946 2,545,671 Passino Mar. 20, 1951 2,589,057 Corson et al Mar. 11, 1952 OTHER REFERENCES Melpolder et al.: Jour. Am. Chem. Soc., vol. 70, March 1948, pages 933-39.

Claims (1)

1. PROCESS FOR THE CONVERSION OF HYDROCARBONS IN PART TO PARA-DIALKYL AROMATIC HYDROCARBONS WHICH COMPRISES IN COMBINATION THE STEPS OF CATALYTICALLY CRACKING ALKYLATE ONTAINED AS HEREINAFTER DEFINED, SEPARATING FROM THE PRODUCTS OF SAID CRACKING A FRACTION CONSISTING LARGELY OF CUMENE WITH MINOR AMOUNTS OF BENZENE, PASSING THE SAID FRACTION TO AN ALKYLATION ZONE WHEREIN IT IS ALKYLATED WITH PROPYLENE, SEPARATING FROM THE RESULTING ALKYLATE BY FRACTIONAL DISTILLATION A FRACTION CONSISTING LARGELY OF PARADIISOPROPYL BENZENE, PASSING TO THE SAID CATALYTIC CRACKING A FRACTION CONSISTING LARGELY OF OTTHO-AND META-DIISOPROPYL BENZENE AND CATALYTICALLY CRACKING THE SAME IN THE PRESENCE OF AT LEAST 50% BY VOLUME DILUENT GAS AT A TEMPERAPERATURE BETWEEN 300* C. AND 425* C. UNDER CONDITIONS WHEREBY VERY LITTLE CONVERSION TO BENZENE, ETHYLENE AND BUTYLENES IS OBTAINED, PASSING THE CRACKED PRODUCT TO SAID ALKYLATION ZONE AS AFORESAID, AND RETAINING THE CONCENTRATION OF ALKYL AROMATICS HAVING OTHER THAN C3 ALKYL GROUPS SUFFICIENTLY LOW IN THE ALKYLATION PRODUCT TO ALLOW SEPARATION OF SAID PARA-DIISOPROPYL BENZENE BY FRACTIONAL DISTILLATION BY WITHDRAWING IN ADDITION TO AND SEPARATE FROM SAID PARA-DIISOPROPYL BENZENE FRACTION A REGULATED PORTION OF THE ALKYLATE BOILING ABOVE SAID PARA-DISOPROPYL BENZENE FRACTION.

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