US2341487A - Manufacture of gasoline - Google Patents

Description

. Feb- 8, 1944- JQF. M. TAYLOR ErAL 2,341,487"

` uANUFAcTunE-OF GAsoLmE Filed lay 27, 1939 lnveni'ors: Jock Francis Mahon Taylor Search Roon MANUFACTURE oF GAsoLINE Jack Francis Mahon Taylor, San Rafael, and

Sumner H. McAllister, Lafayette, Calif., assignors to Shell Development Company, San Francisco, Calif., a corporation of Delaware Application May 27, 1939, Serial No. 276,062

4 Claims. (Cl. 26o-683.4)

This invention relates to the production of improved fuels for gasoline engines and deals particularly with an economical method for producing fuel of high anti-knock value and lead susceptibility from unsaturated hydrocarbons boiling in the gasoline range such as cracked gasoline and the like and with novel hydrocarbon mixtures having such valuable properties.

There is a recognized need for gasoline powdered air and marine craft less subject to re and explosion hazards, and in aircraft a need to overcome vapor lock difficulties such as are encountered as a result of the vacuum created in fuel feed lines and the like during sudden maneuvers at high speed. The perfection of fuel injection devices which can be used successfully to replace earburetion in gasoline engines has created a demand for a fuel of reduced flash point and vapor pressure to meet such need. It is feasible to so fractionate ordinary gasoline as to raise its flash point and make it suitable as a safety fuel as far as volatility is concerned. Such low vapor pressure gasoline has, however, knocking characteristics which render it unsuitable for fuel use. The present invention overcomes this disadvantage and provides safety fuels of high octane value which are remarkably responsive to addition of lead tetraethyl and the like and particularly useful as aviation gasoline free from vapor lock difficulties. It also provides an improved method for producing gasoline of conventional boiling range suitable for use in engines equipped with carburetors.

An important object of the invention is to increase the lead susceptibility and yield of gasoline obtainable from cracked gasoline or suitable fractions thereof and the like. Another object is to produce from such unsaturated products a stable, saturated fuel of high octane rating, and to produce such high quality fuel without undesirable formation of low or high boiling by-products. Still another object is the production of novel hydrocarbon mixtures which do not lose anti-knock value as a result of evaporation, as in storage and the like. Another object is to provide gasoline having a. more uniform octane rating throughout its boiling range. particularly useful in reducing differences in operation of different cylinders resulting from non-uniform gasoline distribution. Other objects will be. apparent from the following description.

In accordance with the present invention these desirable results may be advantageously achieved by reacting a mixture of hydrocarbons boiling within thegasoline range and preferably containing a substantial quantity of normally liquid straight-chain oleflnes with an isoparafiin in the e presence of a suitable alkylation catalyst suchl as concentrated sulfuric acid. In this way saturated addition products of such isoparain with the olefinic content cf the gasoline or suitable fraction thereof being treated, may be formed having higher boiling points than the oleiines from which they are derived. This is contrary to past experience in alkylation with olenes -boiling within the gasoline range which has been confined to highly branched oleiines such as di-isobutylene and the like which yield on reaction with isobutane, in the presence of sulfuric acid, preponderantly products having a boiling range the same as, or lower than, the starting olene as a result of dealkylatlon, splitting or rearrangement reactions which take place under alkylation conditions. We have found, not only that the less branched olefines such as are present in cracked gasoline may be alkylated with isoparafns such as isobutane and isopentane and the like to form valuable higher boiling products but also that by thus increasing the molecular weight of the hydrocarbons, their anti-knock value is not reduced as is usually the case when chain length is extended, but on the contrary, both the octane rating and lead susceptibility of the product may be increased compared with the cracked gasoline fraction from which they are derived.

In order to make the invention more clear it will be described in more detail with particular reference to its application to the reaction of cracked gasoline stock, including fractions thereof, with isobutane in the presence of concentrated sulfuric acid. It will be understood that this implies no limitation on the invention which is also applicable to other hydrocarbon mixtures boiling within the gasoline range and containing a substantial quantity of normally liquid straight-chain oleilnes regardless of their source. Dehydrogenation, for example, may be used in preparing starting material suitable for the present invention. Also other isoparaiiins such. for example, as isopentane, -methyl pentane and the like may be used with the same or other suitable catalysts.

In reacting isoparains with cracked gasoline and the like in the presence of sulfuric acid of alkylationl strength the oleflnes tend to form sulfonates or alkyl sulfates or polymers or other undesirable products which not only reduce the yield of desired alkylated gasoline but also reduce the catalytic activity of the acid. By providing a suitable molecular excess of isoparafn to oleilnes these undesirable side reactions may be suiiiciently suppressed so that the reaction may be made to go predominantly to alkylation and the catalyst protected. Generally molal ratios of lsobutane to cracked gasoline olenes of at least 2:1 are preferred and more preferably ratios of the order of 20 or more to 1. Ratios in the range of 60:1 to 500:1 are particularly useful. It is preferable to pre-mix the cracked gasoline or equivalent starting material with a molal excess of the isoparaiin to be reacted therewith before contacting it with the catalyst acid. A suitable proportion of isobutane is at least two or preferably at least five mols of isobutane per mol of unsaturated hydrocarbon present in the gasoline fraction. More preferably ratios of ten to twenty or more mols of isobutane per mol of olefine are used.

The process is preferably carried out at a temperature below about 50 C. and more preferably in the range of about 20 to about +35 C. It is desirable to operate with the reactants in the liquid phase. Where sulfuric acid is used as the catalyst it is preferable to employ initial concentrations of the order of 85 to about 100% or more preferably 90 to 100% although fuming acid may be used at low temperatures. There appears to be an optimum combination of acid strength and temperature which may differ depending upon the particular oleiines and isoparailin used in the reaction. It is desirable to employ a volume excess of acid over reactants, and more preferably a volume excess of acid over hydrocarbons present in the reaction. About 0.3 to 4 or more volumes of concentrated sulfuric acid per volume of hydrocarbon present may be used although ratios of about 0.7:1 to 3:1 are preferred. It is usually preferable to carry out the reaction rapidly and to avoid further reaction of primary alkylation products with more olefine. Reaction times of a fraction of a minute to about 30 minutes may be used although times of the order of about to 25 minutes are preferred.

Any suitable method of intimately mixing the reactants in the presence of the catalyst acid may be used. Mechanically stirred agitators may be used or the reactants may be flowed through suitable tanks or towers or the like containing packing or baffles capable oi providing the desired intimate mixing. For large scale operations positive circulation by means of a pump or the like may be used to provide the required mixing and the reactor may take the form of a pipe coil or one or more tanks. For example, the reaction mixture may be pumped, preferably under conditions of turbulent flow, to a separator in which sucient stratification is allowed to take place to permit separation of a hydrocarbon phase from which product may be removed equivalent to the feed and the remainder returned for mixing with fresh feed after which the mixture is recontacted with the acid phase and the cycle repeated. In such a system it is unnecessary to completely separate hydrocarbon from the acid in the stratiler. This method of operation has the advantage of providing pre-mixing of the cracked gasoline with a large amount of isoparafln before it is contacted with the acid while also reducing the amount of hydrocarbon which must be removed to separate product from excess isoparaffln compared to once through methods of reaction.

While the process of the invention may be carried out batchwise or intermittently, it is particularly adapted to continuous methods of operation. An especially advantageous method of continuous operation comprises circulation of a stream of reacted mixture through a suitable reaction system and continuously feeding into the circulating mixture the cracked gasoline to be treated and the lsobutane to be reacted there with, the latter preferably in large molecular excess over the olcnic content of the gasoline, while taking off, preferably at a point in the circuit sufciently removed from the feed inlet to insure substantial reaction, reacted mixture from which hydrocarbon equivalent to the feed is withdrawn and the remainder returned to the system. By this method of operation a large recycle of thoroughly dispersed reacted mixture is provided to mix with the cracked gasoline being treated and the acid is maintained thoroughly mixed with isobutane throughout its time of contact with the gasoline so that alkylation of the olefines present in the gasoline is promoted and undesirable reactions such as olefin@ polymerization and/or sulfonation or sulfation are substantially suppressed. It also makes it unnecessary to separate unreacted isopara-flin from the reacted mixture in order to supply the desired large excess thereof in the reaction. Preferably a volume excess of circulating mixture of reaction products, acid and unreacted material over the volume of hydrocarbon feed and most preferably a volume excess of circulating hydrocarbon is used. Such operation provides a mass of circulating liquid so large that the heat of the reaction has but a small effect upon its temperature so that temperature control is easy. The circulating mixture of dispersed hydrocarbon and acid facilitates rapid uniform mixing of the feed with the catalyst in the presence of excess isoparaflln thereby reducing undesirable side reactions. It also reduces the power required for intimately mixing reactants and catalyst. This preferred method of operation has also the advantage of providing more uniform reaction time since inlet and outlet points may be so separated that short-circuiting may be avoided and incomplete or excessive reaction thus reduced.

The attached drawing illustrates, diagrammatically, an assemblage of apparatus which has been found to be particularly advantageous for the manufacture of gasoline in accordance with the process of our invention.

Cracked gasoline or a suitable fraction thereof from a source not shown is supplied by pipe line l to a mixing tank 2 where it is admixed with isobutane and/or isopentane-containing hydrocarbon introduced by pipe line 3. Excess isobutane and/or isopentane recovered from the a1- kylation treatment may advantageously be re turned to the system at this point as by line 4. Reacted hydrocarbon phase containing unrea-cted isoparafn and alkylation products may also be mixed with the feed as by lines 5 and 4. 'Ihe resulting hydrocarbon mixture containing approximately at least 5, and preferably 10 or more,

molecules of isobutane and/or isopentane per molecule of olerie is introduced by pipe line B into a circulating stream of a dispersed mixture of sulfuric acid of alkylating strength and reacted hydrocarbon substantially free of olenes flowing in conduit 1 to the suction end of circulating pump 8. Pump 8 forces the resulting mixture through pipe line 9 and mixing device I0 which may be suitable mixing nozzles or the like, to pipe line II feeding into tank l2 which is proff: Ni

vided with cooling means not shown. Such cooling means may be coils or tube bundles or the like through which any suitable refrigerant may be circulated. Thus, cooling water, brine or liquid butane, for example. may be used as the cooling agent to maintain a reaction temperature of about 10 to 50 C., preferably about 5 to 25 C. Instead of indirect cooling by means of such refrigerants, the cooling may be effected by evaporation of a part of the reaction mixture, for example, isobutane where such isoparaflin is used, or liquefied normally gaseous material may be injected into the mixture and evaporated to maintain the desired reaction temperature. A separate cooling unit in place of, or in addition to, cooling means in tank I2 may be provided either in line 1 or line II to cool the entire circulating mixture or preferably in a branch of the circuit through which a part of the circulating mixture may be by-passed and cooled suiiiciently so that on remixing with the circulating mixture it produces the desired temperature therein.

'Ihe mixture from tank I2, still in a thoroughly dispersed state, passes through conduit I3 which is in communication with conduit 1. Pipe line I4 is provided for withdrawing a part of the dispersion from conduit I3 to separator I5 where stratification of the withdrawn reacted mixture takes place and separated acid phase is returned to conduit 1 by pipe lines I6 and I1. Valve controlled outlet line I8 and inlet line I 8 are provided for withdrawing a part of the catalyst acid. if necessary, and its replacement by fresh or reviviiied acid of suitable strength. 'I'he hydrocar' bon phase formed in separator I is withdrawn by line 20 to a scrubber 2| which is fed with caustic by line '22 to remove any entrained or still emulsified acid. In order to reduce the amount of unreacted isoparaflin separated from reaction product while still providing the desired high ratio of isoparaflin to olefines in the mixture prior to contact with the acid, a part of the hydrocarbon phase in line 20 may advantageously be conducted by lines 5 and 4 to mix with the feed. It is us ually unnecessary to have complete separation of 4 hydrocarbon from the acid in separator I5 and the acid phase returned to the reaction by lines I 6 and I1 may be in an emulsified form with hydrocarbon.

The scrubbed hydrocarbon passes by line 23 t0 a fractionating column 24 in which materials boiling below the initial boiling point desired for the product are removed as overhead through line 25. Such overhead products will contain excess unreacted isobutane and/or isopentane which may advantageously be recycled to the alkylation system. Where sources providing substantially pure isobutane and/or isopentane have been used it is feasible to return such excess directly by lines 25 and 26 to line 4 for admixture with the cracked gasoline to be treated in mixer 2. However, if the original isobutane and/or isopentane contains inert materials such, for example, as the corresponding normal paraflins or the like, it is usually desirable to conduct the overhead from column 24 by lines 25 and 21 to column 28 for removal of such diluents which may be taken ofi by line 25, while the thus purified isobutane and /or isopentane is fed by line 30 to return line 4. Where diluents having a lower boiling point than isobutane are present, another column. not shown, may be used for their removal before the isobutane and/or isopentane is returned to the system. We prefer, however, to use sources of isobutane and/or isopentane free from lower boiling hydrocarbons and for this reason preferably depropanze the isobutane used in order to prevent accumulation of propane in the system. The debutanized gasoline Withdrawn as bottom product from column 24 by line 3l may have any desired initial boiling point since column 24 may be used not only for recovery of isobutane but also for separation of undesired lower fractions of the alkylated gasoline, such separated gasoline components being withdrawn from the system as bottom products from still 28 by line 29. The alkylated gasoline thus recovered by line 3| requires only removal of heavy ends in column 32 in order to obtain a finished product. Such product is recovered through line 33 while heavy ends are removed by line 34.

The following examples of typical applications of the process of the invention to the treatment of gasoline fractions produced by different cracking processes illustrate suitable methods for prac ticing the invention and show its advantages.

Example I Various cracked gasoline fractions were treated in a reactor provided with internal cooling coils and a high speed stirrer and connected with a separator. In each case the reaction system was first charged with sulphuric acid of 98% concentration in the amount required to give the desired acid to hydrocarbon ratio when operating completely full. The liquid feed of cracked gasoline and isoparafiin was supplied continuously while acid layer from the separator was returned to the reaction system, and hydrocarbon phase was removed and fractionated. The reaction temperature was 10 C. and the contact time 20 minutes in al1 cases.

Experiment Number G23 G25 G2 G6 G13 Cracked gasoline used Dubbs cracked gaso- Catalytic cracked Dubbs cracked gaso- Dubbs cracked gaso- Dubbs cracked gaanline boiling range gasoline boiling25 line boiling range lIne boiling range line boiling rango 23 to 70 C. conto 98 C. contain- 23 to 100 C. 23 to 100 C. 23 to 100 C. taining about 50% ing about 70% oleoleiines. ilnes. Feed (weight per cent):

Cracked gasoline l4% 17.5%. 86%-.. 82.5%.

Mol ratio Isoparafn to ole- 10:1 10:1.

fine In feed. Volume ratio of acid to hy- 0.7:1 2:1,

drocarbon. Weight per cent product 135% 116%.

(based on gasoline used). Volumes of product per vol- 3.2 5.9.

ume 0I acid. Bromine No. of product 2.0 0.8.

Gm. Bn per grs. Total sulphur of productm, 0.001% 0.0006%.

Exp. No.

A. S. T. LLECFR octane ra ng:

23-100 C. fraction of product. 100-200 C. fraction of product. Lead susceptibility:

+1 ec. tetraethyl lead per gallon- 23-i00 C. fraction ol product. 100-200 C. fraction f product. +3 cc. teiruetliyl lend per gallon- 23'100" C. fraction of product. 100-200 C. fraction of product.

l By extrapolation.

2 Determined on a 23 to 70 C. fraction. 'i Determined on a 70 to 200 C. fraction.

Example II A West Texas reformed aviation gasoline boiling between 40 and 128 C. which had been phosphoric acid treated and sweetened and contained about 28% olenes was treated in a manner similar to that described in Example I except that 96.5% sulphuric acid was used at C. The

light and has a total sulphur content of 0.001% or less. As will be seen from the results of Example I, the process of the invention is capable of giving novel hydrocarbon mixtures the higher boiling fractions of which have an anti-knock value equal to, or greater than, that of the lower boiling fraction. Such mixtures do not lose octane rating on evaporation in storage and give feed consisted of 57.7 weight per cent of aviation 3" more uniform operation in multi-cylindel` engasoline, 34% of a mixture of isobutane and isogines where the gasoline distribution to the dif- Dentane and 6% of normal butane and pentane ferent cylinders is non-uniform. The products corresponding to a mol ratio of combined isobuof the invention are particularly suitable for tane and isopentane to olenes of 4.2 to 1. The blending with iso-octanes and like high antimol ratio of isobutane and isopentane to oleflnes d" knock value materials in the preparation of gasin the System was greater than 65 to 1. Using oline engine fuels of superior quality. They may a volume ratio of acid to hydrocarbon of 0.7 to 1 also be blended with ordinary gasoline and may a yield 0f 112% by Weight 0f alkylation products be used with di-isopropyl ether and like fuel based on the aviation gasoline was obtained with components. an acid consumption of one volume per 8.48 vol- The higher boiling products produced in acumes of product. The product boiling above 130 cordance with the process of the invention are C. had an A. S. T. MECFR octane rating of particularly useful as safety fuel of low vapo:- 89.8 compared with 72.0 for the depentanized pressure and high quality or as components of original aviation gasoline. such fuel. Thus, for example, products obtained It will be seen from a comparison of columns in Example I boiling between 100 and 200 C. 3 and 4 of Example I that high ratios of isoparmay be used in safety fuel having a flash point affin to oleine in the feed are advantageous in (open cup) of 110 F. or higher and an octane increasing the yield and catalyst life and from rating of 80 to 90 without doping or 95 to over columns 4 and 5 that a volume excess of acid 100 by suitable addition of lead tetraethyl. over hydrocarbons in the reactor is desirable for The invention is capable of variation not only increased yield. A comparison of column 1 with in regard to the unsaturated gasoline which may column 4 shows the materially increased acid be used and the conditions under which the relife obtainable by the use of cracked gasoline action with isoparafn may be conducted but fractions of the type used in these runs having also with respect to the method of operation an end point of 70 C. as contrasted with one of 55 employed. Thus, while the process may be con- 100u C. and point. This was further established ducted so as to give a completely refined, stable by tests made on the separated 70 to 100 C. saturated gasoline in one operation, the use of fraction under identical conditions which gave a suitable auxiliary treatments, such for example. weight yield on gasoline used of 95% and only as preliminary removal of valuable and/or un'- 3.2 volumes of product per volume of acid. The 00 desirable constituents prior to or after alkylasource of the rcracked gasoline may iniiuence the tion may be desirable. Also other agents such, point of fractionation which will give the best for example, as isomerization catalysts may be results. It is usually advantageous to use cracked used either before, during or after the process gasolines having an end point such that the alof the invention. It will therefore be underkylation products all boil within the gasoline stood that the invention is not limited to the range. Cracked gasolinas of 150 C. end point details of operation disclosed by way of illustraor below may be used or more preferably those tion nor by any theory advanced in explanation having end points of not more than about 100 of the more advantageous results attained. but C. Most preferable from the standpoint of long only by the terms of the appended claims. catalyst life are gasoline fractions boiling be- We claim as our invention: low 72 C. 1. A process for producing motor fuel from l By the process of the invention unstable, sour hydrocarbon cracking products boiling in the 3'.; smelling, cracked gasoline of high sulphur congasoline range which comprises fractionating tent may be converted to a Water white, sweet hydrocarbon cracking products to separate a 75 normally liquid fraction boiling between 23 C.

j smelling saturated gasoline which is stable to and 70 C., substantially devoid of normally gaseous olens, and comprising normally liquid, monomeric, straight chain oleflns, from higher boiling components of said cracking products. admixing isobutane with the separated 70 C. end point fraction in the proportions necessary to form a liquid mixture containing at least five mois of isobutane per mol of olein present, and adding the liquid mixture to a circulating dispersion of isobutane and reacted cracked gasoline fraction with about 0.7 to 3 volumes of sul/f furic acid of at least 85% cencentration at about -10 C. to +50 C. while maintaining in the reaction zone a molar ratio of isobutane to olen of 60:1 to 500:1, whereby alkylation of isobutane by said olens with formation of isoparains having four more carbon atoms per molecule than the individual oleiins united with said isobutane takes place and a saturated gasoline of increased lead susceptibility and lowered sulfur content, and which also has a high octane number throughout the boiling range of the reaction products with the octane number of the higher boiling fraction thereof being at least equal to that of the corresponding lower boiling fraction, is obtained.

2. A process for producing motor fuel from hydrocarbon cracking products boiling in the gasoline range which comprises fractionating hydrocarbon cracking products to separate a normally liquid fraction having an end point of not more than '70 C. and comprising normally liquid, monomeric, straight chain olens from higher boiling components of said cracking products, and alkylating added isobutane with said olens by feeding said separated lower boiling fraction and from five to ten mols of isobutane per mol of olefin contained in said fraction into a dispersed mixture of isobutane, reacted fraction and sulfuric ac of 85% to 100% concentration at about -l C. to +50 C., withdrawing reacted mixture after a time of reaction suicient to substantially saturate said oleflnic content while maintaining in the reaction zone a molar ratio of isobutane to olefin of 60:1 to 500: 1 and a volume ratio of acid phase to hydrocarbon phase of 0.721 to 3:1, whereby said oleiins are chemically combined with isobutane to form isoparains having four more carbon atoms per 5 molecule than the individual oleilns united with said isobutane and a saturated gasoline of higher lead susceptibility and lowered sulfur content is obtained which has a high octane number throughout the boiling range of the reaction products.

3. A process for producing motor fuel from 5 hydrocarbon cracking products boiling in the gasoline range which comprises fractionating hydrocarbon cracking products to separate a fraction having an end point below 72 C. and comprising normally liquid, monomeric, straight chain olefns, from higher boiling components of said cracking products, and alkylating an added isoparaflin with said olefin in the presence of a volume excess of concentrated sulfuric acid over the hydrocarbons in the liquidpha'se while maintaining in the reaction zone a molar ratio of said isoparailin to olefin of at least :1 whereby said olens are chemically combined with said isoparafiin to form higher boiling parain hydrocarbons essentially possessing that number of carbon atoms per molecule which corresponds to the sum of the carbon atoms of the individua1 olen and isoparain united and a saturated product of increased lead susceptibility and lowered sulfur content is obtained which has a high octane number throughout the boiling range of the reaction products.

4. A process for producing motor fuel from hydrocarbon cracking products boiling in the gasoline range which comprises fractionating hydrocarbon cracking products to separate a normally liquid fraction having an end point of not more than C. and comprising norfmally liquid, monomeric, straight chain oleflns, from higher boiling components of said cracking products. and alkylating added isoparailin with said olenic content in the presence of concentrated sulfuric acid at 10 C. to +50 C. for a time su cient to substantially saturate the olefinic content of said fraction while maintaining in the reaction zone a molar ratio of said isoparafiin to olefin of atleast 60:1 and a volume ratio of acid phase to hydrocarbon phase of 0.7:1 to 3:1 whereby said oieiins are chemically combined with said isoparailin to form higher boiling parain hydrocarbons essentially possessing that number of carbon atoms per molecule which corresponds to the sum of the carbon atoms of the individual olefin and isoparaiiin united and a saturated product of increased lead susceptibility and lowered sulfur content is obtained.

JACK FRANCIS MAHON TAYLOR. SUMNER H. MCALLISTER.

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