US2310327A - Production of motor fuel - Google Patents

Description

9, 1943- w. J. SWEENEY 2,310,327

' PRODUCTION OF MOTOR FUEL Filed Oct. 28, 1939 Petente Fe. it

rnonncrron or Moron William .Y. Sweeney, Elizabeth, N. ll, assignor to Standard Oil Development Company, a corpo= ration of Delaware Application October 28,, 1939, Serial No. 301,769

3 Glaims.

This invention relates to the production of motor fuel of the gasoline type from higher boil-' ing hydrocarbons and pertains more particularly to a unitary process for the cracking and conversion of hydrocarbon oils into motor fuel of high octane number.

It has, heretofore, been proposed to crack hydrocarbon oils into motor fuel bypassing such oil through the cracking zone in contact with a cracking catalyst such as activated clay or synthetic gels containing silica and alumina. In accordance with conventional practice, the cracked product, after passing through the cracking zone, is fractionated to segregate a motor fuel fraction, a gas oil fraction, and a gas fraction.

When cracking such oil in the presence of catalysts, a considerable excess of butane and butane over and above that which can be directly included into the motor fuel is formed.-

A cracking of oil in the presence of catalysts of the type above mentioned results in the production of a gasoline having a relativelyhigh percentage of olefinic constituents. Particularly is this true with respect to the lower boiling fractions of such motor. fuel.

The relatively high percentage of olefinic constituents present in the gasoline gives an abnormally high acid heat which is considered objectionable in many instances. While the amount of unsaturates present in the motor fuel can be reduced by acid treatment, such treatment normally results in relatively high losses and consequently reduces the yield of motor fuel produced in the process.

One of the principal objects of the present invention is to provide a method for producing gasoline which will have a low acid heat and high yield.

A further object of the invention is to provide a method of producing gasoline in which the excess gases formed in the process are more effectively utilized. Another important object of the invention is to provide a process which will produce a higher yield of gasoline from a given quantity of feed and in which the gasoline produced will have a higher octane number and lower acid heat than is attained by processes heretofore employed.

'Other objects and advantages of the invention will be apparent from the more detailed description hereinafter.

In accordance with some of the more specific phases of the invention, the oil is first cracked in the presence of a catalyst of the type above mentioned, preferably by suspending the catalyst in finely-divided form in a stream of oil to be cracked and then passing the suspension through the cracking zone maintained under temperature conditions for bringing about the desired cracking thereof. The cracked products, after being separated from the catalyst, are then fractionated to segregate a naphtha fraction which is substantially free of aromatics but which contains a high percentage of olefinic constituents and which has a high acid heat. This fraction is then passed through an alkylating unit in admixture with iso-parafins wherein the olefins present are caused .to react with the iso-parafins to form a saturated product having a low acid heat.

" In accordance with a more specific phase of the invention at least a part of the isoparafins employed for alkylating the naphtha olefins are obtained from the cracked products.

According to another more specific phase of the invention the aromatic-free naphtha fraction is obtained by fractional distillation or condensation of the cracked products although the invention in its broader phases comprehends the separation of aromatics from the naphtha by other means. When fractional distillation or condensation is employed to form an aromaticfree naphtha fraction the end point of the naphtha should be below F. and preferably somewhat iower.

Having set for the objects and general nature, the invention will be best understoodby reference to the accompanying drawing which is a diagrammatic illustration of an apparatus suitable for carrying the invention into effect.

Referring to the drawing,- the reference character l designates a feed line in which the oil to be cracked is introduced into the system. The oil to be cracked may be a condensate stock such as virgin or cracked gas oil or a residual stock such as topped or reduced crude. The oil introduced through line i is forced by means of pump 2 through a heating coil 3 located in furnace t. The oil during its passage through the heating coil 3 is heated to a temperature to vaporize at least a large portion thereof and to preheat such vapors to the desired reaction temperature. The oil after passing through coil 3 is conveyed through transfer line 5 to a separator 6 wherein vapors separate from unvaporized residue. Any residue collected in separator 6 is removed therefrom through line i.

Vapors separated in the separator i is removed overhead through line 8. In case clean condensate feed stocks are charged to the unit the separator I may be omitted or the vapors may be by-passed around the separator through line 9.

The vaporized oil from lines 8 or 9 are then passed'through lines Ill and II to a reaction chamber l2.

Prior to passing to the reaction chamber l2, there is injected into the oil stream to be cracked a powdered cracking catalyst, such as, for example, acid treated adsorbent clays such as Superfiltrol or synthetic adsorbent compoundscontaining silica and alumina. As illustrated in the drawing, the reference character I3 designates a catalyst hopper from which the finely divided catalyst is fed by means of a suitable feeding mechanism such as a star feeder l4 capable of feeding the powdered material at a controlled rate to a suitable transfer mechanism such as a screw conveyor l5 which injects the powdered catalyst into the oil vapors to be cracked. The relative amount of the catalyst injected into the oil stream will vary over a relatively wide range depending upon the nature of the feed stock, the activity of the catalyst, the amount of conversion desired, temperature of the reaction zone, and other factors. In general, the amount of catalyst should vary between 0.3 and 20 parts of catalyst per part of oil by weight.-

The suspension of powdered catalyst in oil vapor. is transferred through line H to the reaction chamber I2 in which it is maintained for a period sufficient to effect the desired conversion of said oil into lower boiling hydrocarbons.

For illustrative purposes I have shown the reaction chamber l2 in the form of a heat exchanger having a tubular coil '16 through which the suspension passes. The tubular coil I3 may be surrounded by a suitable heat exchange medium such as molten salts or molten metal capable of maintaining the reaction chamber at the desired temperature.

The temperature of the reaction zone may, for example, range between 700 and 1000 F. and the time of contact of the suspension in the reaction zone may range between 2 seconds to 2 minutes depending upon other variables such as nature of the feed stock, activity of the catalyst,

and other factors.

While the reaction chamber has been shown in the form of a heat exchanger, it will be understood that the invention is not limited to any particular type of reaction chamber and that any suitable type capable of maintaining the powdered material in the desired suspended condition, may be employed.

The suspension of cracked products and the powdered catalyst, after passing through the reaction coil [6 in the reaction chamber l2 passes to a transfer line I1 leading to a suitable solid gas separator which for illustrative purposes has been shown in the form of a cyclone separator H3.

The powdered catalyst separated in the cyclone separator I8 collects in the bottom thereof and may be discharged to a suitable feeder, such as a star feeder 18a capable of maintaining the desired pressure on the cracking system. The catalyst removed from the cyclone separator l8 may be regenerated by suitable equipment, outside of the purview of the present invention and recycled to the catalyst hopper i3, or a part or all of the catalyst may be recycled directly without regeneration,

While there has been shown a single cyclone separator for removing the powdered catalysts from the cracked vapor, it will be understood that other types of separating equipment may be employed. It is desirable to remove substantially all of the powdered catalyst before subjecting the vapors to condensation and to this end a plurality of cyclone separators may be arranged in series if desired for effecting more complete removal of the catalyst from the oil vapors.

The cracked vapors,'after having the powdered catalyst 'removed therefrom, are passed through line l9 to a. suitable fractionating tower 20 wherein the cracked vapors are segregated into a plurality of different fractions. Insufiivciently cracked constituents boiling above the end point of the desired motor fuel are condensed in the bottom section of the fractionating tower 2D and withdrawn therefrom through line 2|. This product may be removed through line 22, or it may be recycled to the cracking zone for further cracking. In the latter case,- the condensate formed in the bottom of tower 20 is passed through lines 2|, 23 and pump 24 to the heating coil 3.

In accordance with one of the phases of the present invention, a heavy naphtha fraction,

' boiling between about F. and about 400 F.,

is segregated from the cracked products. To this end, the upper portion of the fractionating tower 2|] may be provided with a trap on tray 29 and the temperature of the top portion of the fractionating tower above the trap on tray 29 is preferably controlled by means of a suitable heat exchanger or reflux medium to condense the heavy naphtha constituents. The heavy naphtha collected in the trap on tray 29 may be withdrawn therefrom through line 30 as a final product of the process.

One of the important phases of the present invention is to control the top temperature of The products from the condenser 32 then pass.

to a receiver 33 in which the liquid condensed in the condenser 32 separates from residual gases. The residual gases comprising principally hydrogen, methane, and ethane and ethylene, together with a small amount of the higher molecular weight hydrocarbons are released from the system through line 34. The licuid distillate comprising chiefly propane-propene, butane-butene and light naphtha constituents boiling up to about 170 F. collected in receiver 33 is withdrawn therefrom through line 35 and treated as hereinafter described.

For simplicity there has been shown in the drawing a simple condenser 32 for condensing the propane-propene and butane-butene fractions along with the light naphtha fractions. It will be understood, however, that in large scale operations it may be desirable to condense only the light naphtha fractions in the condenser 32 and to then pass the gases from the receiver 33 containing all normally gaseous fractions to an absorption system wherein the propane-propene and butane-butene fractions are selectively absorped from the gases. Or if desired the absorption may be carried out to segregate only the butane-butene fraction and this product formed from the catalytic cracking process of the nature hereinbefore described contains a high percentage of olefinic constituents and isoparafiins containing a tertiary carbon atom, such as isobutane, isopentane, and the like.

Referring again to the drawing, the distillate collected in the receiver 33 withdrawn therefrom through line 35 is passed through line 33 and 31 and pump 38 into a reaction chamber 39 containing an alkylating catalyst capable of bringing about the reaction between isoparaffin and oleflnic constituents; Such a catalyst may comprise, for example, sulfuric acid of high concentration such as between 95 and 110%, fluosulfonic acid formed by reacting hydrofluoric acid with sulfur trioxide, chlorosulphonic acid metallic halides such as aluminum chloride, zinc chloride, ferric chloride, with or without the addition of hydrochloric and other halogen acids,

activated clays, boron fluoride, and the like. For illustrative purposes, it will be assumed that the catalyst contained in the reaction chamber 39 is fluosulfom'c acid. The fiuosulfonic acid is introduced into the chamber 39 through line 39a which merges with line 31 leading to orifice jets 49 capableof effecting intimate dispersion of the oil to be treated in the acid-hydrocarbon mixture contained in the reaction chamber 39. The temperature within the reaction chamber 39 is preferably maintained between 50' and 150 F. and under a pressure sufficient to maintain the oil in liquid phase under temperature conditions within the reaction zone.

The oil undergoing treatment, after passing through the catalyst contained in reaction chamber 39 in finely dispersed form, separates as a separate phase on top of the acid and is removed from the reaction chamber through line M. A portion of the oil so removed and containing entrained acid is preferably recycled to lines 32, 33, and pump 38 back to the reaction chamber for controlling the contact time to obtain the desired reaction. A part of the oil so withdrawn is passed to line 45 to an acid settler 33 wherein entrained acid may be separated from the reaction product. The amount of products recycled as compared with acid introduced into the acid settler may range between 5 and 15' parts or higher recycled to one part introduced into the acid settler. This amount, however, will vary depending upon the desired time of contact within the reaction chamber 39 and can be controlled readily by manipulation of valves located in the lines t5 and 42.

Acid separating out in the acid separator 49 is withdrawn from the bottom thereof through line 91 and may be rejected through line 48 or a part or all thereof may be passed through line 69 which merges with line 43 and recycled to the reaction chamber 39.

Reaction products segregated from entrained acids'in the acid settler 46 are removed there'- irom through line 5i and passed to suitable distilllng and fractlonating equipment for segregation of the desired motor fuel fraction therefrom. As illustrated, the products from line 5! pass through a heat exchanger 52 wherein the products are heated to a temperature sufiicient to vaporize all motor fuel constituents boiling below the desired end point thereof. Products from the heat exchanger 52 thereafter pass to a combined distilling and fractionating chamber 53.

Liquid productsv boiling'above the desired end point of the motor fuel are collected in the bottom portion of the tower 53 and withdrawn therefrom through line 54. If desired, this product may be withdrawn from the system through lines 55 and 56. According to one of the phases of the present'invention, however, this productis passed to the catalytic cracking unit through lines 51, 23, and pump 24, to heating coil 3. This product forms particularly desirable charging stock to the catalytic cracking unit.

As a further alternative, the higher boiling fraction collected in the bottom of tower 53 may be recycled to the: reaction chamber 39 and combined with products treated therein. To this end, the products withdrawn through line 54 may be passed throughline 58, cooler 59 and pump 69 to the inlet side of the reaction chamber 39.

As illustrated, tower 53' is provided with a trap out tray 6| and the temperature in the upper section of the fractionating tower above the trap out tray is controlled to condense the desired motor fuel therein. The motor fuel fraction collected in the trap out tray 91 may be withdrawn from the tower through line 62. I o

It ,has been found that this product, as compared with the light naphtha fractions collected in the receiver 33 isconsiderably more saturated, and has, consequently, a much lower acid heat and higher lead susceptibility. Furthermore, this improvement in acid heat and lead susceptibility is accomplished without sacrifice of yield, but, on the contrary, with an actual increase in yield due to the union of the normally gaseous hydrocarbons with the light naphtha fractions treated. For example, the yield may be as high as 120 to 150% depending upon the relative amounts of oleflnic and isoparamnic constituents present in the feed.

If desired, additional isoparaffins or olefins may be introduced into the light naphtha fractions passing to the reaction chamber 39 through line 63.

The following examples illustrate the advantages which may be realized by carrying out the present invention. It will be understood, however, that the values and conditions given in the examples are illustrative rather than limitive.

Example A blend of catalytically-cracked gasoline produced by employing a powdered catalyst, comprising finely divided acid treated clay of the type known as Super Filtrol, suspended in the oil vapors to be cracked was first formed from five runs under different operating conditions as follows:

In the first run, an East Texas gas oil of 33.4 A. P. I. gravity was cracked at an average temperature of about 895 F. employing a weight ratio of catalyst to oil of 1 to 1 and a contact time of about 2'7 seconds. The amount of 400 E. P. gasoline formed was about 35%.

In the second run, the same feed stock was cracked at an average temperature of about 900 F. employing a weight ratio of catalyst to oil of about 0.7 to 1 and a contact time of about 24.5 seconds. The gasoline conversion in this case amounted to 27.3%.

In the third run, the same feed stock was cracked at an average temperature of 950 F. employing 0.6 weight ratio of catalyst to oil and a contact time of 24.5. The gasoline conversion was 34.1.

In the fourth run, the same feed stock was cracked at a temperature of 950 F. employing a weight ratio of 1.0 part of catalyst per part of oil and a contact time of 28 seconds. The gasoline conversion in this case amounted to 39.7%.

In the fifth run, the same feed stock was cracked at a temperature of 950 F. employing 1.6 parts of catalyst per part of oil by weight and a contact time of 33 seconds. In this case, the conversion amounted to 46.6% gasoline.

The blend of gasoline formed from the above runs was fractionated to segregate a light fraction amounting to the first 18% of the gasoline and boiling up to 160 F. This fraction had a bromine number of 91 and contained nearly 50% of oleflnic constituents. The blending value of this product in a reference fuel indicated an octane number of 84.9.

This product in admixture with isobutane was treated with fluosulphonic acid of commercial strength of from 95-100% over a period of 40 minutes, with 20 minutes additional stirring. The fluosulphonic acid amounted to 5% of the total hydrocarbons and the amount of isobutane used was twice the volume of the naphtha treated. The product was then allowed to settle and the hydrocarbons separated from the acid. The

boiled below 400 F.. the remainder boiling above 400 F. The amount of gasoline formed from the light naphtha amounted to 114%, thus showing an actual increase in the amount of gasoline recoverable. The bromine number of the gasoline product obtained was showing complete saturation and consequently a low acid heat. The 57-265 F. aviation fraction had an A. S. T. M. octane number of 86.5 which was higher than the octane number of the light naphtha treated. Furthermore, the addition of 1 cc. of tetraethyl lead raised the A. S. T. M. octane number from 86.5 to 98.6 showing that the 5'7265 F. fraction had an extremely high lead susceptibility.

Having described the specific embodiment, it will be understood that the invention embraces such other variations and modifications that come within the spirit and scope thereof.

What is desired to be protected by Letters Patent is:

1. A method of producing gasoline having a low acid heat, high octane number lead response by conversion of higher boiling hydrocarbons which comprises passing the oil to be converted through a cracking zone containing an active cracking catalyst and maintained at cracking temperature, keeping said oil in contact with said cracking catalyst within said cracking zone for a period sufficient to convert a substantial portion of said oil into motor fuel constituents, thereafter separating from the cracked products a light naphtha fraction substantially free of aromatic constituents and containing a substantial amount of olefinic constituents having a high acid heat, passing the fraction so segregated in a mixture with isoparaffins in such proportion that the molar ratio of isoparaflins to olefinic constituents is not less than one to one in contact with an active alkylating catalyst capable of accelerating the union between isoparafi'ins and olefins to form a saturated product and maintaining said mixture in contact with said catalyst for a period suflicient to alkylate a substantial amount of said olefins in said light naphtha fractions and to increase the boiling range thereof.

A method of producing gasoline having a low acid heat, high octane number lead response by conversion of higher boiling hydrocarbons which comprises passing the oil to be converted through a cracking zone containing an active cracking catalyst maintained at cracking temperatures, keeping said oil in said cracking zone in contact with said catalyst for a period sufficient to convert a substantial portion of said oil into motor fuel constituents, thereafter fractionating the cracked product to segregate a light liquid product substantially free of arcmatic constituents and containing a relatively high proportion of isoparafiin having four or more carbon atoms to the molecule and a high percentage of olefins having at least three carbon atoms to the molecule, and a heavier naph-- tha fraction, passing said light naphtha fractlon through a reaction zone containing an active alkylating catalyst capable of accelerating the union between the isoparafiins and the olefins to form higher boiling products of saturated character and having a lower acid heat and thereafter combining alkylate formed from said last-named treatment with said heavier naphtha fraction separated from said cracked products to form a gasoline of the desired boiling range and volatility.

3. A process for the conversion of hydrocarbon oils to form gasoline having a low acid heat, high octane number and lead response which comprises passing the oil to be converted through a cracking zone maintained at active cracking temperature, contacting said oil within said cracking zone while at active cracking temperature with a cracking catalyst, keeping said oil in contact with said catalyst for a period sufficient to convert a substantial portion thereof into gasoline constituents, thereafter separating a light naphtha fraction substantially free of aromatic constituents and containing a relatively high concentration of olefins and a heavy naphtha fraction from the cracked products, passing the light naphtha fraction so segregated through an alkylating zone containing an active alkylating catalyst, introducing isoparaifins into said alkylating zone in an amount at least equal to the amount of olefins contained in said light naphtha fraction to thereby maintain a'molar ratio of isoparafiins to olefins of at least 1 to 1, maintaining said alkylating zone under conditions such as to cause said isoparafiins to unite with said olefins to form a saturated alkylate product, and thereafter combining alkylate formed from said last-named alkylating treatment with heavy naphtha from said catalytic cracking treatment to form a gasoline blend containing light naphtha alkylate and heavy catalytically cracked naphtha.

WILLIAM J. SWEENEY.

Images