US2008468A - Production of motor fuels - Google Patents

Description

Julyl6, 1935.. I IR. H. PRICE 2,008,468

PRODUCTION OF MOTOR FUELS Filed Aug. 24, 1932 T Cmlcirgg l mmaaa QC}? INVENTOR fli /Le ATTORNEY Patented July 16, 1935 UNITED STATES PATENT OFFICE 2,008,468 PRODUCTION OF MOTOR FUELS Ralph H. Price, Hammond, 1116., assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana 7 Application August 24, 1932 Serial No. 630,256

1 Claim.

5 covery of said benzol from said gases after cracking.

atures. This process has not, however, been carried out on a continuous and commercial scale. One of the difiiculties with the commercial operation of this process has been the dif iculty of economically recovering the benzol from 'the cracked gases. On cracking a gas such as propane at temperatures between 1350 F. and 1700 F. and at pressures between 0 and lbs. per square inch above atmospheric yields of two gallons or more of benzol to 1,000 cu. ft. of original gas may be obtained; As a by-product, however, there is obtained almost an equal amount of heavy, higher boiling materials and tar. Furthermore, the final gaseous mixture due "to the formation of methane and hydrogen has from 1.5 to 2.0 times the volume of the original gas. The difliculty of recovering benzol at a concentration of only 1 gal. or thereabouts per 1,000 cu. ft. of final gas and in the presence of an almost equal amount of heavy tar is very great. Simple cooling and condensation will not give an economically high percent recovery of benzol and an oil scrubbing or other absorption operation must therefore be employed.

The presence of the tar, however, greatly complicates such absorption operations. The gas must be thoroughly cooled before such absorption treatment and the tar deposits on cooling surfaces and prevents sufficient heat transfer during said cooling. Furthermore, it is impossible to completely condense tar from such gaseous mixtures, small amounts thereof persisting as a fog throughout the cooling step. This causes contamination of the subsequent scrubbing or adsorbent medium and consequent deposition of gummy and pitchy materials on heat interchanger surface.

I have discovered that these difiiculties may be avoided and the recovery of benzol from such cracked gases accomplished efficiently and economically by the use of pressure still charging stock as a cooling and scrubbing medium for these gases. By pressure still charging stock I refer to hydrocarbon oils of petroleum origin which are destined for treatment in conventional oil cracking systems. This may include materials commonly known as virgin gas oil, cycle gas oil, naphtha bottoms, crude oil, or fuel oil, etc.

I have discovered that if benzol is recovered by absorption in such scrubbing mediums which are then subsequently treated in conventional oil cracking systems the benzol passes through the w oil cracking systems unaltered and is recovered in admixture with the gasoline produced therein, thus enhancing the antiknock value of said gasoline. This avoids all separate handling of the benzol and simplifies construction and operation of the system greatly. Furthermore, heavy tarry materials which escape the preliminary cooling step (as fog, etc.) in appreciable quantities, would make the operation of an ordinary oil absorption system for benzol recovery almost impossible due to their building up in the system. In my process, however, these tarry products do not impede operations as they pass through the cracking system and are eliminated with other tarry products therefrom.

The operation of my improved process may be briefly described as follows: I crack hydrocarbon gases from any convenient source under the pressure and temperature conditions aforementioned.

The hot gases are passed from the reaction tubes or soaking drum into a primary cooler and tar separator. In this cooler the gases are partially cooled by any convenient means but preferably by direct spray of a relatively small amount of charging stock sufiicient to cool the gases partially and to precipitate most of the tar content while itself being essentially completely vaporized. Subsequent to the primary cooler the gases are passed to a final cooler and scrubber where they are completely cooled and stripped of their benzol content by contact with relatively large volumes of charging stock.

Optionally, another cooler may be inserted between the primary and secondary coolers, this cooler being ordinarily of the indirect water-coil type. Since most of the tar has been eliminated in the primary cooler this indirect cooler is not subject to rapid loss of efficiency from tar deposi' tion.

The charging stock from the secondary cooler scrubber is passed directly to a conventional oil cracking system and the dissolved benzoltherein is recovered in solution in the gasoline produced therefrom.

My invention will be understood with reference to the attached drawing which forms part of this specification and which represents a diagrammatic elevational view of suitable apparatus for carrying out'my process.

Operation of my process in detail is as follows:

Referring to the drawing, hydrocarbon gas, preferably consisting of or containing. large amounts of ethane, propane or butane enters through pipe Ill and is heated in heater I i to temperatures of 1350 to 1700" F. while maintained under pressures of 0 to 100 lbs. per square inch above atmospheric. The hot exit gases pass through valve l2 and insulated soaking drum 13 or through valve I4 and by-pass l5. In either case the hot gases enter primary cooler H5 at a low point thereof. The gases in cooler l6 are cooled by any suitable means but preferably are cooled, mainly at least, by the vaporization of charging stock therein. The charging stock is supplied from pipe I! and is distributed to cooler 16 through valve I 8 in line l9. As stated, however, other cooling means may be employed in cooler l6, and in particular it is sometimes desirable to remove the hot'tar from outlet 20, cool same and pump same (cooler and pump not shown) back into cooler l6 through inlet 2| in orderto cool gases therein. In any event, the amount of charging stock added through line I9 is so regulated that essentially all is vaporized and relatively little passes out with the con-- densate through oiftake 20. Depending on the cooling conditions, the character of the charging stock and the nature of the particular set-up, the temperature of the gases leaving cooler l6 may lie between 400 and 800 F.

The benzol-containing gases leaving, through line 22 may be passed in one of two directions. They may pass through valve 23 in line 24 and valve 25 in line 26 into the final scrubber cooler 21 in which they are contacted directly with a relatively large volume of charging'stock introduced through valve 28 in line 29. Internal coil coolers may be provided in this tower and the quantity of charging stock charged thereto is so adjusted that the gases leaving are cold and stripped of their benzol content.

Alternatively the gases in line 22 may be passed through valve 30 in line 3| and may be further cooled in cooler 32 prior to their introduction into the final scrubber 21. Cooler 32 will ordinarily be of the indirect water cooled type and any condensate produced therein will be removed through drain 33. The cooling in cooler 32 will ordinarily be adjusted so that condensate removed through drain 33 is relatively free of henzol, but if necessary this condensate may be further stripped of benzol as a separate operation.

In either modification the total stripped gas leaves the scrubber 21 through line 34 and a portion of this gas may be recycled through valve 35 in line 36 and mixed with gas entering the cracking step in line In, or it may be eliminated through vent 31. Scrubber 21 is preferiably operated at 50-400 pounds per square inch gage pressure, and if the heater ll 'be operated at a pressure lower than this, a compressor may be placed in line 26. i

The relatively cool charging stock and dissolved benzol from scrubber 21 is drawn off through line 38 where it may mix with additional charging stock from line 39 and is then picked up, with or without intermediate storage (not shown) by pump 40 and passed into a conventional oil cracking system. As illustrated in the drawing, the total charging stock passes through heat exchanger 4| in line 42 and enters the '2-section bubble tower 43 in the upper part of the lower section. The total charging stock is partially or substantially completely vaporized in this section by the vapors of hot cracked products and passes through line 44 into the upper section of the tower wherefrom clean charging stock is removed through line 45 by pump 46 and passed through the preheating, heating and soaking coils of furnace 41. Cracked products are returned to the bubble tower 43 through line 48 and tar is eliminated from the tower through line 49. The mixed vapors of cracked gasoline and benzol leave the tower through line 50 and pass through heat exchanger 5|, cooler 52 and into high pressure separator 53, the fixed gases being eliminated through line 54 while total condensed products are withdrawn through 55. The pressure on the liquid products is reduced in line 55 and they are passed into a low pressure separator 56 from which liquid products are withdrawn through line 51. Fixed gases are eliminated from the system through valve 58 or are recycled through valve 59 in line 60 to the gas supply in line W for the gas cracking step in heater ll.

The foregoing description of the cracking system is conventional and I may use any suitable system or arrangement of apparatus such that the benzol and the cracked gasoline are recovered in admixture with each other, and preferably that any tar absorbed from the gas cracking step is eliminated from the charging stock prior to the oil cracking step.

The gas charged to the gas cracking system through line l0 may be natural gas, or refinery gas (i. e. gas produced by distillation, cracking, or weathering of petroleum and its products), but I prefer to use a gas containing relatively low proportions of methane since this compound is undesirably stable and does not yield large amounts of benzol except at very high temperatures. I therefore prefer to use gases containing relatively high proportions of hydrocarbons having 2, 3 or 4 carbon atoms.

I have previously stated that the conditions of the gas cracking step in heater 1 l and/or soaking chamber I3 may lie in the range of temperatures from 1350-1750 F. and pressures of 0-100 pounds per square inch above atmospheric. Somewhat higher pressures, such as 200-300 pounds may be used within the same-temperature range without essential alteration of results but with some economies in furnace construction. I may also use appreciably higher pressures, such as 500 pounds or more, in which case lower temperatures may be used, such as l000-l350 F.

In the operation of coolers l6 and 32 I have previously referred only to the use of direct cooling by vaporization of hydrocarbon oils, such as charging stock, and to indirect cooling by water. I may, however, so design and operate my oil cracking system as to permit charging a mixture of oil and water thereto in which caseI may use direct water cooling in whole or in part incooler 16 (through line 2 I) or in scrubber 32 (through a connection not shown). In cooler 21 I may or may not make use of indirect cooling coils (not shown). Wherever the term charging stock is used herein or in the claims hereof I refer to hydrocarbon oils of petroleum origin suitable for cracking into gasoline which may include crude oil, relatively heavy uncracked residual oils, light or heavy gas oil, naphtha bottoms, kerosene, etc.

The foregoing is a full and complete description of my invention.

I claim: g

The process of producing motor fuel which comprises subjecting normally gaseous hydrocarbons to elevated temperature and pressure to effect a conversion of said gaseous hydrocarbons to normally liquid low-boiling hydrocarbons of a benzenoid character, cooling the products of such conversion and removing said normally liquid low-boiling hydrocarbons therefrom by scrubbing said products with a relatively heavy absorbent hydrocarbon oil, removing the thereby enriched absorbent oil, convectively distilling it in a stream of hot cracked vapors to vaporize said low-boiling hydrocarbons and substantially all of the clean constituents of said absorbent oil, dephlegmating the combined vapors thereby obtained to remove therefrom a clean charging stock comprising relatively heavy constituents having boiling points above the end point of the desired low-boiling product, removing said charging stock, subjecting it to cracking conditions to produce vapors of cracked products therefrom, delivering the cracked vapors to the convective distillation stage to supply the convective dis-' tillation medium therefor, removing vapors of low-boiling products, comprising products obtained by conversion of normally gaseous hydrocarbons and by cracking of said clean charging stock, from the dephlegmation zone and condensing them to recover the desired motor fuel product.

RALPH H. PRICE.

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