US2353490A - Cracking and reforming of hydrocarbons - Google Patents

Description

July 1l, 1944. J. NooRDuYN CRACKING AND REFORMING OF HYDRCARBONS Filed July 21, 1941 2 sheets-sheet 1 July 11, 1944.

J. NooRDu YN CRACKING ND REFORMING OF HYDROCARBONS Filed July 21, 1941 i 2 sheets-sheet 2 www@ miri NL nvznfo: Jan Noordugn Patented July 11, 1944 Y' CRACKING AND BEFORLIING F HYDBOCARBON S v Jan Noorduyn, Emmastad, Curacao, Netherland West Indies, Company, of Delaware assignor to Shell Development San Francisco, Calif.,

a corporation Application July 21,'1941, Serial No. 403,331 Claims. (01.'198-66) 'I'his invention relates to the manufacture ofv motor fuels by cracking of hydrocarbon distillates and especially to the art of cracking low octane naphtha to produce an-improved motor fuel of high anti-knock value.

It is well known that by subjecting naphthas of low octane rating to high temperatures and pressures the naphthas are cracked so that gasolines having higher octane numbers are produ'ced. At the same time varying amounts of products having boiling points too high and too low to be incorporated in the gasolines are formed resulting in reduced yields of the improved gasolines.

It is also known that as the thermal treatment becomes more severe. i. e., the temperature, pressure, residence time or combinations thereof are increased, the octane number of the treated gasoline is, within limits; further improved and its yield further decreased. When a certain severity of the thermal treatment is reached, deposition of coke in the diierent parts of the cracking apparatus becomes so rapid that further useful operation is impossible.

It is known also that more severe cracking conditions can be maintained without objectionable coking by introducing into the cracking zone. together with the naphtha, gaseous hydrocarbons such as those having 'one to five carbon atoms in the molecule. In general, however, very large quantities, i. e., 100% or more, of these gases had to be used to obtain substantially improved operation, an expedient which very appreciably raised the cost of heating, compressing and pumping.

'I'he object of this invention is to produce improved motor fuels by reforming or cracking hydrocarbon distillates or naphtha inthe presence of certain addedl normally gaseous hydrocarbons. Other objects are to make use of the cracking in. the presence of added hydrocarbon gases at reduced cost and to utilize certain less valuable hydr'ocarbon gases for this purpose. Further objects include the transformation' of less valuable gases into more useful ones. Still further objects will be found in the improvements hereinafter disclosed.

This invention is based on the discovery that the addition of relatively small amounts of normal paramnic hydrocarbons having four and five carbon atoms to a distillate oil or naphtha makes possible the practical application of an appreciable increase in the severity of cracking conditions and that at the same time these light hydrocarbons are transformed into others which are more useful. l

According to this invention, a relatively heavy feed, i. e., a hydrocarbon distillate oil, is commingled with about 10% to 30% or more of a lighter feed comprising predominantly parailln .hydrocarbons having four and five carbonatoms in the molecule and preferably consisting essentially of normal butane and normal pentane.

'I'he commingled hydrocarbons are then sub'- jected to heat and pressure to result in cracking, and the treated hydrocarbons are-separated into heavier-than-gasoline products. gasoline and lighter products. The heavy part is withdrawn and may be utilized to suit convenience. 'I'he gasoline has improved anti-knock properties and may be treated. blended and utilized in any con.- ventional manner. The lighter-than-gasoline products may also be withdrawn and utilized conventionally. but it is more advantageousto separate the butanes and pentanes, and preferably the normal butane and pentane, therefrom and to use them alone or in admixture with other C4 and Cs parailln hydrocarbons for the above-mentioned light feed, while remaining oleilnes and other gases may be put to any desirable useful purpose.

The preferred way of producing these butanes and pentanes is to separate from the cracked product a fraction comprising predominantly hydrocarbons of four and five carbon atoms in thev molecule and subject it to polymerizing and alkylating conditions so as to produce unsaturated gasoline by polymerization of theV olenes and saturated gasoline by alkylating isoparalns witholenes. Simultaneously, the normal paraiins are prepared for the light feed to be used in the above cracking operation. l

The term fcracking" as herein used is meant to cover thermal non-catalytic reactions resulting in carbon-carbon scission or dehydrogenation, or both. and thus includes reforming." In this process the conditions of temperature, time and pressure depend on the exact result desired. In general, it is possible to, and I do, maintain conditions more severe than those maintainable without rapid coking if the heavier distillate were charged alone. as a result. of which a greaterv increase in octane number can be secured than is normally possible.

The hydrocarbon distillate which is the heavy feed of this process may be any gasoline, naphtha.

gas oil, etc.. or a fraction thereof. boiling within Straight run distillates, especially from parai'linic crudes, are very suitable.

When it is desired to further improve the octane numbers of cracked distillates, it is preferable to remove highly unstable components formed incidentally during the cracking operations, such as those generally known as gumf forming compounds, e, g., diolefines, certain branched and other highly reactive oleflnes,

' styrene, etc., because they are most prone to dichlorethyl ether, SO2-benzene mixtures, etc.,

ox' by a combination of solvent and anti-solvent .such as phenol or cresol with propane, etc.; by

treatment with adsorption agents such as clay, bauxite, fullers earth, diatomaceous earth, silica gel, etc., preferably at elevated temperatures below incipient cracking; by sulfuric acid orphosphoric acid treatmentat suitable concentrations to produce a sludge containing the undesirable constituents which can be separated; etc.

If desired, suitable selected distillates formed within the process may be recycled to the cracking zone to form .part of the heavier feed. This may be especially useful if a substantial proportion of the heavy feed introduced into the: system boils above the gasoline boiling range, and after cracking gives a middle oil distillate heavier than gasoline. The recycle oil, like the cracked naphtha. may be treated to remove coke-forming substances as described. Recycle oilsof high aromatic contents but low oleiine contents frequently aid in reducing coke deposition by virtue of their solvent power for tars before they are converted to coke.

The light feed ,normally constitutes between and 30%, as already stated, and preferably to 25% of the total feed. This light feed comprises predominantly butanes and pentanes, preferably normal butane andv normal pentane, and may contain substantial amounts of hexanes, preferably normal hexane. It is desirable that it be substantially free from olefines. A preferred composition is one containing less than 5% olefines,V over"50% "of normal pentaneand over 35% of normal butane, the remainder being predominantly hexane.

The following considerations serve to explain some of the factors which are believed tcl contribute to the success of this process.

objectionable deposition of coke in cracking coils andother .parts of the apparatus is probably due to formation of heavy aromatic. and tarry materials during cracking, which materials readily separate from the heated hydrocarbons, especially in the skin layer which exists along heating surfaces. As a result these tarry materials deposit on the heating walls where they stick and progressively are 'transformed into coke.

It is generally believed that the harmful cokeforming tars are produced from the initial feed by recurring cracking or dehydrogenation, and

polymerization. Lower oleiines, particularly the branched ones, undergo these reactions much more rapidly than corresponding parafllns, and by eliminating them from the feeds and especially from the light feed, the tendency to form tars and coke within the time required to raise the octane number of the cracked gasoline to a cer-r .tain predetermined level is greatly diminished.

It is already known that the tendency for tars (once they are formed) to deposit from a hydrocarbon mixture under cracking conditions can be lowered by adding thereto normally gaseous hydrocarbons at elevated pressures. I have found that C4 and C5 hydrocarbons are Particularly valuable from this point of view, as apparently under the conditions maintained they are effective in much lower concentrations than the still lower hydrocarbons. It is for this reason that a material increase in the severity of crack'- ing conditionsabove the normal limits can successfully be maintained in the presence of rela- .tlvely small amounts only of the preferred light feed. While, if desired, amounts in excess of about 30% of the total feed may be introduced, the excess oi the light feed above about 30%'has little, if any, additional beneficial efiecton the octane number improvement, while the cost of the treatment increases more nearly proportionally with increases in the amounts ofthe added light feed. L

The normal saturated hydrocarbons which comprise the light feed are of relatively little value in the manufacture of polymer and alkylation gasoline as they are too unreactive. However, when they are subjected, together with gasoline, to 'the intense cracking conditions of my process, part of them at least undergo transformations such as isomerization, dehydrogenation, cracking, and possibly polymerization, etc., so that more valuable hydrocarbon gases are produced. C3 and lighter paraffin hydrocarbons, being more stable thermally, do not undergo transformations as useful under the same conditions.

As indicated above, the cracked gases resulting Y from this process, being rich is reactive components, are subjected to polymerization or alkylation, or both. If desired, the polymerization of olefines and alkylation of olenes with isoparamns can be achieved as part of the lthermal reaction taking place during cracking by including them in the light feed. In general, however, this is not very desirable as it involves less controllable and less efllcient reactions than the separate polymerization and alkylation of selected fractions, y.particularly when employing moderate temperatures below cracking in conjunction with catalysts. Moreover, as pointed out, the introduction of olenes into the cracking zone as part of the light feed is liable to defeat in part at least the very purpose of this invention because they are prone to speed up coke formation. Furthermore, separate alkylation and polymerization processes result in an efficient separation of olenes and isoparafflns from the normal parailins and thus furnish the preferred light feed of this process.

The .process of this invention is illustrated in the accompanying drawings which represent specified flow diagrams of two alternative forms of this process. Figure I discloses the combined polymerization and alklation of the C4. and C5 cuit. Figure II shows the separate polymerization and alkylation of the C4 and Cs cut.

In Figure 1, a suitable relatively heavy feed, i. e., a hydrocarbon distillate from a source not shown, and a lighter feed having a composition as hereinbefore defined 4are introduced through conduits I and I, respectively, into pipe 2.

The light feed may comprise predominantly gases produced within the process, as will be described later, admitted through conduit 8, or, it desired, gases from an outside source not shown (such as a stabilizer for straight run gasoline) introduced through line 4. or both. If 'the light feed contains substantial amount of C: and lighter components, it maybe advantageous to scrub it with the heavier feed under conditions to absorb In the latter mainly the pentanes and the butanes, thereby producing the desired mixed feed, or else the light and heavy feeds may simply be mixed and compressed by conventional means not shown.

The mixed feed in conduit 2 proceeds to cracking coils 8 in furnace 1 in which the desired conditions of temperature, time and pressure are maintained to eifect'the cracking. Depending upon the compositions and the proportions of the heavy and light feeds,suitable temperatures and pressures may vary between about 950 F. and 1100 F. at 500 to 2000 pounds, and preferably between 1000 F. to 1050 F. at 800 to1200 pounds. These temperatures refer to exit temperatures, while the pressures refer to pressures at the entrance of coils 8. 'I'he time of cracking may be controlled with the aid of a reaction chamber, not shown.

The heat-treated hydrocarbons now pass by way of conduit 8 to fractionator l wherein they are separated into the different fractions ln the usual way. i. e., tar and heavydistillates boilf ing above the motor fuel range which are withdrawn 'through line I0 and a lighterfraction including motor fuel which is taken overhead through line II.

The overhead products from fractionator l are further separated in fractionator I2 to which line II leads. 'I'he bottom product which is a cracked naphtha or gasoline distillate containing hydrocarbons of six,or more carbon atoms is withdrawn through line I4, while the gas fraction withdrawn through line I6 contains the Ca hydrocarbons and lighter components. 'I'he C5 and lighter fraction is further separated In fractionator I8 to produce a light gaseous fraction composed essentially of Ca and lighter components, e. g., hydrogen, methane, ethane, ethylene, propane and propylene, which is taken overhead through line 22, and a bottom fraction comprising predominantly hydrocarbons having four or f ive carbon atoms, which is withdrawn' through line 20.

'lJhe C; and lighter fraction is withdrawn from the process and may be utilized in any desired manner not shown.

'Ihe C4-C5 fraction may, if desired, be eliminated from the process ,through line 24 provided a suitable light feed is introduced into lthe system in sufficient amounts from an outside source, not shown, through line 4. However, it is preferred to proceed as follows:

The Ci-C fraction from fractionator 'Il enters a polymerization plant 28 through line 20 where it is subjected to polymerizing conditions in the presence of a polymerization catalyst, for example, to a temperature of about 440 F. to 500 F. and a pressure of about 500 to 1000 pounds p. s. i. over a solid phosphoric acid catalyst. Preferably, the polymerization isregulated so as 'to predominantly polymerize iso-oleflnes, leaving normal oleflnessubstantially unchanged.

25 stantially all of the oleiines. alkylation plant is by-passed.

TheV resulting'hydrocarbons are fractionated to separate the polymer gasoline which is withdrawn.

Remaining gases are than further treated in an alkylation plant 2l to react the normal olefines with isoparamns, for example, in the presence of concentrated sulfuric acid under alkylating conditions, thereby producinga high octane number saturated gasoline which is sepal0 rated from the gases unaffected by the reaction and withdrawn. Normally,the isoparaflln content of this gas is lnsuilicient to alkylate all of the oleflnes present and therefore isobutane may have to be admitted to the alkylation plant through line 28 from a. source not shown. Moreover, as is well known, the best alkylating conditions require in the reaction zone the presence of a large excess of the isoparafllns over the olenes, and after completed reaction this excess is separated from the residue gases and Instead of polymerizing, or polymerizing and `alkylating, the C4-Cs fraction as described, I may first fractionate it to produce a fraction 30 consisting predominantly of C4 and another of Cs hydrocarcarbons, respectively, which fractions may be processed separately by the above methods, as shown in Figure II. I

Cracking furnace 1 and fractionating columns '8, I2 and Il are exactly the same ln Figure II as in Figure I. The difference lies in the addition of column 30 for the separation of the Cl-Cs fraction withdrawn from the bottom of column I8 through line 20. This fraction is con- .40 ducted through line 28 into the column 30 and the C4 fraction is withdrawn from the top of this column through line 3i or 32, andthe Ct fraction is withdrawn from the bottom oi' this column through line 33 or I4. The C4 fraction 48 from the fractionator 30 enters the polymerization plant I5 through line 22, where it is sub- Jected to polymerizing conditions in the presence of a polymerization catalyst, as previously described, and similarly the Cs fraction from frac- 50 tionator 20 enters the separate polymerization plant 31 through line 34, where it is subjected to polymerizing conditions in the presence of a polymerization catalyst. The advantage of separating the C4 from the C fraction for separate polymerization is that different polymerizing treatments may be employed so as to obtain the highest yield of desired products from each.

Remaining gases may then be further treated in alkylation plants I6 and 38 respectively, to

00 react the normal oleflns with isoparaillns, for

example in the presence of concentrated sulfuric acid, under alkylating conditions, thereby producing a high octane number saturated gasoline, vwhich is separated from the gases unaffected by c5 the reaction and withdrawn..

Furthermore, isopentane being itself a valuable component of motor fuels, I may recover it from the pentane fraction and blend it with gasoline. In this case, isobutane from an outslde'source may be used for alkylating the normal pentenes.

Residual gases from the -above separations usually consist mainly of normal .pentane and normal butane. 'I'hey are returnd to the crack- 78 ing operation through line 5.

2,171,207, and other references; alkylation ofl aromatic or isoparamnic hydrocarbons by olefines in the presence of similar catalysts; hydration of olefines to alcohols in the presence of acids, or their oxidation in the presence of metal catalysts as silver. or their halogenation. hydrohalogenation, etc.

The following data from plant scale operation further illustrate my invention:

Straight run Venezuelan naphtha was cracked under conditions close to coking aloneand then in the presence of a light feed. The following table gives comparative results and shows that while the yields of cracked gasoline have been diminished. its octane n umber is raised and the amount oi' high grade polymer and allwlate gasoline available is increased.

Couven Im roved tional crac ing oi cracking invention Percent light feed on intake 19. 9 Percent C; in light feed cn intake..... 0 10.73 Percent Ci in light leed on intake. 0 6. 52 Cracking coil outlet temperature, F 1.013 1,049 Cracking coil inlet pressure. pounds.-. 900 900 Percent yield on naphtha intake:

Cracked gasoline 07. 7 59. 2 n-C and n-Ci araillns 3.3 14. 2 Polymer gasol e available from iso-C. oleilnes 2. 8 4. 8 Alkylate goline available from remaining C3C-C| oleilnes... 14. 7 32.4 Octane number oi cracked gasoline 76.4 79. i) Average octane number oi polyi nier and alkyiate gasolinas 90 'iotal yield ci gasoline 85. 2 96. 4 Octane yield l 750 8, 020

l Octane yield-sum ci products oi octane numbers r yields o! the several gasolinas.

I claim as my invention:

l. In the process of cracking hydrocarbon distillates,r the improvement comprising commingling said distillates with a light feed to produce a mixture, said light feed constituting between about 10 and 30% of said mixture. consisting essentially of normal butanes and normal pentanes, and produced at least in part of said process, subjecting said mixture to non-catalytic cracking in a cracking zone at a temperature between about 950 and 1100 `F. and a pressure between about 500 and 2,000 pounds p. s. i., fractionating the resulting cracked products to obtain at least two fractions, a gasoline distillate and a lighter fraction consisting essentially of hydrocarbons of four and ve carbon atoms and containing oleflnes and isoparaiins. treating said lighter fraction to convert said olefines and isoparaillns to ,higher boiling products, separating said products from residual gases, and returning at least apart of the latter to said cracking zone.

2. In the process of cracking hydrocarbon distillates, the improvement comprising commingling said distillates with a light feed to produce a mixture. said light feed constituting between about 10 and 30% of said mixture, consisting es- 75 sentially of normal butanes and normal pentanes. and produced at least in part in said process. subjecting said mixture to non-catalytic cracking in a cracking zone at a temperature between about 95o and 1100 F. and a pressure between about 500 and 2,000 pounds p. s. i., fractionating the resulting crackedproducts to obtain at least two fractions, a gasoline distillate and a lighter fraction consisting essentially of hydrocarbons of four and ilve carbon atoms and containing olefines and isoparaillns, subjecting said lighter fraction to polymerizing and alkylating conditions to convert -said olefines and isoparaillns to higher boiling products. separating said products from the residual gases, and returning at least a partof the latter to said cracking zone.

3. In the process of cracking hydrocarbon distillates. the improvement comprising commingling said distillates with a light feed to produce a mixture, said light feed constituting between about 10 and 30% of said mixture, consisting esjecting said mixture to noncatalytic cracking in a cracking zone at a temperature between about 950 and 1100 F. and a pressure between about 500 and 2,000 pounds p. s. i.. fractionating the resulting cracked products to obtain at least two fractions, a gasoline distillate' and a lighter fraction consisting essentially of hydrocarbons of four and ve carbon atoms and containing oleilnes and isoparafns, subjecting said lighter fraction to polymerizing conditions in the presence of solid phosphoric acid catalysts and to alkylating conditions in the presence of sulfuric acid to convert the major part of said olennes and isoparains to motor fuels, separating said motor fuels from residual gases, and returning at least a part of the latter to said cracking zone.

4. In the process of cracking hydrocarbon distillates, the improvement comprising commin gling said distillates with a light feed to produce a mixture, said light feed constituting between about 10 and 30% of said mixture. consisting essentially of normal butanes and normal pentanes, and produced at least in part in said process. subjecting said mixture to non-catalytic cracking in a cracking zone at a temperature betweenV about 950 land 1100 F. and a pressure between about 500 and 2,000 pounds p. s. i., fractionating the resulting cracked product to obtain at least three fractions, a gasoline distillate and two lighter fractions. one consisting essentially of hydrocarbons of four carbon atoms and the other of hydrocarbons of nve carbon atoms, both containing oleflnes and isoparaiins, treating said latter fractions to convert said olenes and isoparaillns to higher boiling products, separating said products from residual gases, and returning at least a portion of the latter to the said cracking zone.

5. In the process of cracking hydrocarbon distillates, the improvement comprising commingling said distillates with a lightwfeed' to produce a mixture. said light feed constituting between about 10 and 30% of said mixture, consisting essentially of normal butanes and normalpentanes. and produced vat least in part in s aid process. subjecting said mixture to non-catalytic cracking in a cracking zone at a temperature between' hydrocarbons of four carbon atoms and the other ot hydrocarbons of ve carbon atoms, both containing olennes and isoparamns; treating the C4 lighter fractions to convert the olenes and isoparailns contained therein to higher boiling products and separating said products from residual gases; treating the C lighter fractions to convert the olefinescontained therein to higher boiling products, separating said products and subjecting the remainder of said C5 fraction to fractional distillation to separate isopentane from residual gases; and returning part atleast of the 5 residual gases so obtained trom said lighter fractions to said cracking zone.

JAN N OORDUYN.

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