US2253665A - Hydrocarbon conversion processing - Google Patents

Description

Aug. 26, 1941.

V. VOORH EES HYDROCARBON CONVERSION PROCSSING Filed JuneV 20, 1938 lNvENToR Unoier'oeer oorhees LMA/m' ATTORNEY PatentedAug. 26, 1941 HYDROCARBON CONVERSION PROCESSING Vanderveer Voorhees, Hammond, Ind., assigner to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application June 20, 1938, Scral'No. 214,68l

12 claims.

This. invention relates to the lmanufacture of motor fuels and particularly -to the conversion of heavier hydrocarbon oils into gasoline and light hydrocarbons boiling within the gasoline boiling range. One object of the invention is to increase the reaction rate in the conversion process. Another object of the invention is to increase the yield and quality ofA the gasoline obtained.

In the `cracking of gas oil it is well known that the cracking rate Aor rate of gasoline production is a function of the temperature to which the oil is heated and also .the character of the oil under' going treatment. Certain oils, particularly the more paraflinic oils, are said to be easy cracking, i. e., more readily converted into gasoline by a single passage through the cracking furnace. Other oils, especially cracked gas oil, recycle stocks, etc., are more diflicult t convert into gasoline. When excessively high temperatures are used to increase the rate of conversion, dimculty is encountered with coke formation which may b e suiciently serious to clog the cracking apparatus and force a shut down.

The invention is illustrated by a single drawing which shows schematically, in elevation, an apparatus suitable for carrying out the process.

According to my process, there is'added to the charging stock undergoing cracking an accelerating or promoting agent which consists chiefly of the polymerization products of the butylenes, particularly polymerized isobutylene. This promoting agent may be produced in various ways but I prefer to effect the polymerization of the butylenes with the -aid of catalysts. For this purpose I may use sulfuric acid, phosphoric acid, active metal halides, of the Friedel-Crafts type, e. g., aluminum chloride, boron trifluoride, etc.

As an example of the method of producing the cracking promoter, liquid isobutylene is treatedr with about 0.2 to 0.5% of BFa with agitation'licare being taken to control the temperature.VJ Various temperatures may be employed, f or example room temperature or temperatures from to 40 F. Still lower temperatures maybe used.

The polymerization product'is normallyfa liquid A and may be a light oil or a viscous, semi-solid plastic. It may be separated from the catalyst and dissolved in the cracking stock previously mentioned. The amount employed will vary usually from l to although somewhat larger amounts than 10% may be vused if desired and amounts as littleas 0.1% may have a useful effect. Referring to the drawing, the cracking reaction is preferably carried out in a pipe furnace I0 where the oil is rapidly brought up to the .desired cracking temperature, for example 900 to 950 F. The oil may be maintained for a short time, e. g., from 10l seconds vto 5 minutes at the elevated temperature in a soaking coil or unflred soaking chamber I I, after which the products are separated by distillation in tower I2 in the usual ,manner to remove the unvaporizable residue or tar by line I3, gasoline and gasby lines I4 and I5 respectively. The intermediate fraction heavier than gasoline is recycledby 4line I6 and pump I'I for further cracking.V l

The cracking stock introduced `by line I8 may consist of gas oil, for example, Mid-Continent or California gas oil, reduced crude oil, or partly cracked stock` boiling within the gas oil boiling range, commonly called cycle stock or naphtha bottoms. The charging stock may also be a heavy naphtha fraction-boiling largely within the gasoline boiling range which is being treated to increase the knock rating by the socalled reforming process. When cracking such'a stock higher temperatures will usually be employed, e. g., 950 to 1100 F.

Instead of adding the butylene polymer promoter directly to the cracking stock entering the heaterby line I9, for example I may add itto the stock after the heating has progressed to a large extent and the oil has reached the cracking temperature, e. g., 900 to 950 F. Thus, in the case of a cracking process employing a heating coil and soaking chamber I may add it to the oil leaving the heating coil and entering the soaking coil or soaking chamber for example, by line 20 in the drawing. The isobutylene polymer` is conveniently handled in a solution for this purpose, a solution in a portion of the cracking stock being suitable. Thus, a solution of 25% of the polymer in cracking stock may be injected into the hot stream of oil entering the soaking chamber or soaking coil. The` polymer solution added in this way is preferably preheated to 300 to 500 F. before introducing into the soaking The promoter-polymer may be obtained by polymerization of the isobutylene contained in the hydrocarbon gases producedin the promoted cracking process hereinabove described. Thus,

referring to the drawing, gases may be `Withdrawn from the gas separator by line 2| and forced by compressor 22 into gas fractionator 23 Where the propane and lighter gases are eliminated by line 24. The liquid C4 fraction containing isobutylene may be led by line 25 to polymerizer 26 wherein the isobutylene is polymerizedv with a suitable catalyst as described. The polymerized isobutylene may then' be conducted by line 21 to soaking chamber Il wherein it is mixed with the hot hydrocarbons from heater l undergoing conversion.

In the preparation of the olefin polymer promoter, I may employ a butane-butylene fraction` separated by distillation from a hydrocarbon gas, for example, -a gas derived from a cracking process. The C4 fraction may suitably contain both normal butylene and isobutylene and a small portion of normal butylene may be polymerized along with the isobutylene in the preparation of the promoter. If the promoter is prepared by polymerization at very low temperatures, for example, -80 to 100 F. 'it will contain hydrocarbons of very high molecular weight, for example, 100,000.to 500,000, along with lighter hydrocarbons having molecular weights as low as 1,000 to 5,000. If desired, I may subject this initial polymerization product to a fractionation process, preferably by treating with selective solvents as described in my Patent 2,073,506, or by distillation in vacuum, and I may employ only the lower molecular weight fractions for pro-v moting the cracking process. I may also polymerize the isobutylene with sulfuric acid of suit'- able strength and under conditions to yield principally the dimer and'trimer, in which case the product may be separated by fractional distillation, the dimer being distilled off for use as a motor' fuel of high knock rating andthe heavier f products, consisting chiefly ofY the isobutylene trimer, being employed as a cracking promoter. However, because of the high volatility of these light polymers they are diilicult to handle, especially in liquid phase cracking and, therefore, I prefer to employ the heavier polymers previously referred to, having molecular weights of 500 to 2500 or higher, which remain in solution in the cracking stock until the decomposition temperature is reached.

Although the exact mechanism of the reaction of isobutylene polymers with hydrocarbon oils undergoing cracking is not fully understood, it is believed that the polymers undergo rapid decomposition at the high temperature prevailing `in the cracking process with the formation of free radicals whose energy is available for initiating the decomposition of the associated hydrocarbons, somewhat in the manner of a chain reaction. The decomposition products of the isobutylene polymers unite with the decomposition products of the oils undergoing' cracking, thereby yielding a gasoline product having an altered configuration from that obtained in the absence of the promoter. As a result, the`gasoline obtained from the promoted process will possess a higher knock rating than ordinary cracked gasoline` produced from the same charging stock under the same cracking conditions.

Although I have described my process as applied to conventional thermal cracking reactions, it should be understood that other modifications of the process may be employed. Thus, I may employ catalystsin the cracking process and conduct the reaction at somewhat lowertemperai tures.

For example, when using chromium oxide, boron siiicate, hydazea` aluminum silicate, fullers earth, etc., as catalysts, I may conduct the cracking reaction at` temperatures within Athe range of 800 t0 925 F., in which case a suitable catalystv chamber provided with temperature regulating means may be introduced in place of the soaking chamber Il previously mentioned.

Various petroleum-oils, as indicated,lmay be converted in to gasoline in my process, including paraillnic, naphthenic and aromatic gas oils, crude residues, etc. I prefer to conduct the conversion under pressure, for example, `200 to 1000 lbs. per square inch, maintaining th oil in the liquid phase. I may employ two or more chargjected to a suitable conversion temperature, com- 'y prising heating said heavy oil to said conversion temperature, then, before any separation takes place, introducing a small amount of a polymer of .isobutylene prepared by the treatment of liquid isobutylene with a catalyst of the Friedel- Crafts type, thereafter further subjecting said heavy oil and said isobutylene polymer to conversion temperaturesseparating gasoline from the products of conversion and recycling products heavier than gasoline to said conversion process. A

2. In the process of` converting high boiling paraflinic hydrocarbon oil into gasoline of high knock rating wherein vsaid oil is subjected to high conversion temperatures of about 900 to 1100L7 F. and the products of said conversionvare fractionated to remove said gasoline therefrom, the method of increasing the rate ofy conversion of'said parainic hydrocarbon oil, comprising effecting said conversion by introducing into said oil undergoing heating at a point of conversion about 0.1 to 10% of a polymer of isobutylene resulting from the treatment. of liquidisobutylene at ordinary and lower temperatures with a catalyst of the Friedel-Crafts type.

3. The process of claim 2 wherein the catalyst employed in polymerizing said isobutylene is boron fluoride.

4. The process of claim 2 wherein said isobutylene is polymerized at a temperature within the range of about 0 to 40 F. v

5. The process of claim 2 wherein said conversion is conducted at a pressure of about 200 to 1000 pounds per square inch.

6. In the process of converting# heavy hydrocarbon oil in to gasoline wherein said oil is subjected to heat and pressure until a vsubstantial portion is converted into gasoline and the products are then separated by .distillation and unconverte'd fractions of the oil are` recycled to the heating step, the improvement comprising introducing into said oil undergoing heating at a point of conversion, a conversion promoter co'mprising a high boiling polymer of isobutylene sensitive to decomposition at said conversion temperature, said polymer beingderived from the treatment of liquid isobutylene with a Friedel- Crafts type catalyst.

' 7. The process of claim 6 wherein the said high boiling isobutylene polymer is introduced in an amount equal to 0.1 to 10% of the hydrocarbon l oil treated.

oil treated.

9. ,The processof claim 6 wherein isobutylene is recovered from the hydrocarbon gases obtained from the said conversion operation, subjected to polymerization and the resulting isobutylene polymer isintroduced into said conversion heat# y ing step.

10. The process of claim 6 wherein said isobutylene polymer possesses a molecular weight of l1. The process of claim 6 wherein said iso- 5 isobutylene.

butylene polymer possesses ya molecular weight within the range of 5,000 to 500,000.

i2. The'process of claim 6 wherein said'iso

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