US2131169A - Cracking and extracting hydrocarbon oils with a selective solvent - Google Patents

Description

Sept. 27, 1938. E. F. ENGLISH 2,131,169 CRACKING AND-EXTRACTING HYDRCARBON OILS WITH A' SELECTIVE SOLVENT Filed Nov. 21, 1954 2 Sheets-Sheet 1 PA R T/A A -n t: .BUBBL-A.

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Sept. 27, 1938. l F. ENGLISH v 2,131,169

CRACKING AND EXTRACTING HYDROCARBON OILS WITH A SELECTIVE SOLVENT Filed Nov. 21, 1934' 2 sheets-sheet '2 f 72d v www H- Gf 9 2 f CooLL-:n

t oaLen RATP/IVA TE LINE 7b2 A c T/o/vA rf/v'a To WE E A Cou/V752 CQPRENT SEPARATOR ExmAdv-lo/v Towel COIL .SGLVENT' Ll E l I '-vL 2 60 Patented Sept. 27, 1938 7 UNITED vSTATES CRACKING AND EXTRACTING HYDROCAR- BON OILS WITH A SELECTIVE SOLVENT Edward F. English, Baton Rouge, La., assignor to Standard Oil Development Company, a. ccrporation of Delaware Application November`21, 1934,'$erial No. '154,026 1 claim. (c1. 19d-5o) This invention relates to a process of treating hydrocarbon oils, such as the various mineral oils including petroleum oils, shale oils, oils ob'- tained in the low temperature carbonization ofv coal, hydrogenated Aoily products, etc. by the combination of a cracking and a solvent extraction process, and will be fully understood from the following description when read in conjunction with the drawing, the sole figure of which is a diagrammatic side elevation partly in section of an apparatus appropriate for carrying out the invention.

The main object of the present invention is to ysubject the hydrocarbon oil to a cracking process, to separate a cycle stock from the cracked products, this cycle stock being a distillate product boiling higher than the naphtha obtained in the cracking process, to subject this cycle stock to a treatment with a selective solv vent for separation thereof into a more parafnic and a less paraiiinic product, and to subject these two products to dierent kinds of treatments.

Referring now to Fig. 1, the same will be described in conjunction with the method of op- 'erating the apparatus illustrated. The fresh feed, such as for example, gas oil, is pumped from storage tank I through partial condenser 2 and heat exchangers 3 and 4 into the accumulator 5. The raiilnate from the solvent extraction step is also passed into the accumulator, as will be described hereinafter. 'Ihe mixed feed from the accumulator is fed through high pressure intercondenser 6 and heating coil 1 into the soaking drum or reaction chamber 8. The mixed 36 feed is heated' to the cracking temperature in coil 1 and undergoes the desired extent of, crack` ing in the soaking drum 8. A limited amount of cracking usually takes place in the heating coil. Ifdesired, the soaking drum may be omitted 4l) from the circuit, the coil temperature being raised to increase cracking in the heating coil and compensates for loss of cracking in the soaking drum. The cracked eiiiuent from 8, after partial release of the pressure, is discharged into 45 the separator 9 which may be provided with various fractionating devices, such as discs and doughnuts. Tar is withdrawn from the separator through cooler III into a storage tank (not shown). Vapors from the separator ipass 50 through the high pressure intercondenser 6 and,

y through heat exchangers 3 and 4 into the lower part of a. bubble tower II. Part of a heavy cycle stock condensed in intercondenser 6 and/or part of the cycle stock from heat exchangers 3 and 4 55 may either be returned to the separator 9 or withdrawn from the unit-through cooler I2 or passed to a solvent extraction unit. The bubble tower Il is provided with eiilcient fractionating means, such as bubble cap plates, and serves for the separation of the naphtha with the `desired endpoint as overhead product. The naphtha vapors are passed through the partial condenser 2 and final condenser I5, into the receivers I6- Ia, provided with vents for the release of gases through lines I1 and I8. Part of the naphtha is returned to the top of the bubble tower II through line I 1a as a reux for the control of the fractionation. The liquid product obtained at the bottom of the bubble tower II is a cycle stock which is run through heat exchanger I9 and cooler I9a into the mixing tank I4 of the extraction unit. As cooling medium in cooler I9a water or chilled brine or other suitable cooling medium may be used to reduce the temperature of the cycle stock from bubble tower II to below that at which cycle stock and solvent are completely miscible. The temperature 'at which extraction is carried out is selected'to give the desired character of extract and/or raiiinate. The selective solvent from storage tank 20 `is passed to the mixer I4 and thoroughly admixed with the cycle stocks, after which the mixture is forwarded to the settling tank 2| in which separation into two layers, 'viz, railnate layer and extract layer takes place. The/so-called raffinate layer consisting of the more parainic constituents of the cycle stock together with some dissolved solvent, is reheated in reboiler section 22 arranged in the saine furnace as heating coil 1, and then discharged into the stripping tower 23 on which a vacuum is preferably maintained. The selective solvent is` obtained as overhead vapor condensed in condenser 24 and returned to the selective solvent tank 20. The solvent-free raiiinate is then passed to fthe accumulator 5 for recracking. Alternatively, all or part of the raiiinate may be removed from the system through line 25 into a storage tank (not shown) and used for themanufacture of Diesel oil, heating oil or similar products. -The extract layer which consists of the selective solvent and non-paraiiinic constituents extracted from the cycle stock is reheated in heat exchanger I9 and then passed through the release valve 26 to tower 21. -In this tower the selective solauxiliary cooler subsequent to condenser 28 to further cool solvent before return to mixer Il.

The extract removed as bottoms from tower 21 is introduced into the vacuum stripper 29 in which the remainder of the selective solvent is removed as overhead product condensed in condenser 30 and returned to the storage tank 20. 'I'he extract is removed from the bottom of the stripper 29, cooled in cooler 8| and then passed to `a storage tank 34 for various uses to be explained further below. Alternatively, the extract may be subjected to cracking under conditions different from those used in the cracking of the mixed feed. Other methods of utilizing the extract are shown diagrammatically'and consist of either submitting the same to hydrogenation in the hydrogenation unit 35 or to a chemical treatment in the chemical treatingunit 36.

Referring to Figure 2, fresh feed is withdrawn from tank 50 by means of pump l5I and forced through heating coil 52 in furnace 53. The heated oil is then passed through line 54 into a separator 55 fromV which the heavy tarry products are withdrawn through line 56'. vapors ,from separator 55 are withdrawn through 58, from which gasoline vapors are removed through line 59, passed through a cooler Sllandk thence passed through line 6| into a gasoline storage tank 62. 'I'he heaviest fractions in tower 58 are withdrawn through line 63. An intermediate fraction or cycle oil is withdrawn from tower 58 through line 64 and introduced into a countercurrent extraction tower 65. A suitable selective solvent contained in storage tank 65, is withdrawn by means of pump 61 and forced through line 68 into the top of tower 65. Rainate is removed from tower 65 through line 68 and introduced into a still 10 in which the hydrocarbons are distilled from the solvent in the event that the solvent used is higher boiling than the hydrocarbon fractions. It will be understood that if the solvent used is lower boiling than the hydrocarbons, the solvent will be distilled from the hydrocarbons in still 10. The hydrocarbon vapors are removed from still 10 through line 1l and after passing through a vcooler 12, are passed through line 13 into the fresh feed tank 50. The solvent is removed from st ill 10 through line 14 and returned to the solvent supply tank 86. A

The extract is removed from tower 65 throug line 15 and introduced. into a still 16 in which the solvent is separated from the hydrocarbons by distillation. As indicated above, if the solvent is higher boiling than the hydrocarbons, the latter will be vaporized, and if the solvent is lower boiling than the hydrocarbons, the solvent will be vaporized. The hydrocarbon vapors are removed from still 16 through line 11 and collected in extract storage tank 18. The solvent is removed from still 15 through -line 19 and returned to the solvent supply tank 66.

The extract is Withdrawn from tank 18 by pump 80 and passed through line 8| into a second heating coil 82 in furnace 83, wherein the extract is cracked at a higher temperature than the fresh paraiiinicfeed oil in heating coil 52. The heated oil from coil 82 is passed through line 84 and merges with the heated oil from coil 52 flowing through line 54.

The selective solvent may be any of those known to be effective in the separation of a hydrocarbon oil 'into more parailinic and less The' parafllnic constituents. Usually the extract removed by the selective solvent contains the unsaturated naphthenic and aromatic constituents, while the raffinate consists ofthe more parafllnic constituents. We may cite phenol, the several cresols, aniline, furfural, nitrobenzene, triphenyl phosphate, triorthocresyl phosphate, liquid sulfur dioxide, etc. as examples of selective solvents which may be used in the carrying out of the present process. Instead of one solvent a mixture of them may be used; for example, a mix-v ture of phenol with cresols. The action of the selective solvent may also be modified by the addition of other organic or inorganic solvents such as, for example, water, alcohols, glycol, etc. 'I'he `extraction step consists of mixing the cycle stock to be extracted with, say, an equal volume or more of the selective solvent, thoroughly agitating the mixture, then allowing separation of two layers to take place at a temperature below extract layer are then separated from each other and the selective solvent is removed from both layers, usually by means of distillation, but other means, either physical or chemical, may also be used.

The cracking part of the present process may be carried out in the liquid phase at a pressure of several hundred pounds per square inch, say between 250 and 1,000 pounds per square inch, or even at pressures higher than that, or in the vapor phase at comparatively low pressures approaching atmospheric pressure. The temperature may be any of the usual cracking temperatures or may be considerably higher than say 1,000c F. although, in many cases, it is preferred to carry out the present process at medium temperatures, say between 800l,000 F, The arrangement described above and illustrated in the drawing is a tube and tank cracking system, but other systems may also be used. Further, the arrangementl shown may be modified in various ways; thus, for example, when the fresh feed is a dirty stock, such as a topped crude, it may first be preheated and then fed into the separator 9 Ainstead of into the accumulator 5.

The raiiinate is usually returned to the cracking system as a cycle stock and fed for this purpose into the accumulator 5. However, part or the whole of the raffinate may be removed and used for various purposes, suchas Diesel fuel, heating oil, furnace oil, etc. The extract may be subjected to cracking under conditions different from those used in the main cracking system composed of heating coil 1 and soaking drum 8. jected to hydrogenation or to various chemical treatments thus, for example, it may be treated with sulfur for the preparation of wood preservatives, fngicides and insecticides. It may also be treated with `,various inorganic oxides or sulfides; for example those of arsenic, zinc, mercury, etc. for the same purposes.

By the present process the cycle stock is separated into a rafiinateuwhich shows improved characteristics for certain uses such as, for example, Diesel oil and an extract which again is a more appropriate raw material for certain other uses than the untreated cycle stock. To illustrate the point the extract is a better raw material for treatment with sulfur than saturated hydrocarbons, because the latter produce a large amount of H2S in their reaction with sulfur. The extract is also an excellent raw ma- It may also be withdrawn and subin the presence of a catalyst and in a vapor phase at temperatures between 950-1050 .F. whereby a naphtha having excellent solvent qualities is obtained.

- The following examples are given to illustrate the above: v

1. A paraiiinic gas oil is cracked, the products being gasoline, fuel oil, gas and cycle stock. The rst three are withdrawn from the unit, the cycle stock is subjected to'soivent extraction with a mixture of phenol and glycol and separated into rainate and extract. The ralnate is suitable for cracking with a relatively high gasoline yield and is therefore mixed with fresh feed and returned to the cracking process. The extract is suitable for the production of high octane blending stock and is cracked at high temperature in the separate crackling circuit 32-33, the distillate from which latter cracking may be blended with the primary cracking products or may be segregated for use as blending stock to improve the octane number of other distillates. g.

2. 'I'he parafllnic gas oil may be cracked and separated into raffinate as Vin Example 1, the rainate being returned with fresh feed to the cracking process. The extract being more reactive chemically than either the fresh feed or the ramnate is submittedl to sulfurization or arsenication.

3. The c gas oil is cracked and therafvflnate is returned to cracking as above. The

, cracking stock or high grade Diesel fuel. 1f subjected to destructive hydrogenation in the presence of a catalyst at a temperature of say between 950 and 1050 F., it will yield solvents and `toxic oils, the former suitable` for the preparation of varnishes and the latter for use as wood preservatives, disinfectants and as raw materials for thel manufacture of explosives and dyes.

The following specific example will illustrate my invention: 18,750 gallons per hour of 30 A. P. I. gas oil (completely miscible with aniline at 175-185 F.) fresh feed are passed into the accumulator 5, after being preheated in 2. 3 and I to about 500 F. The mixed feed is pumped from the accumulator at a temperature of about 440 F. and after being preheated in the high pressure heat exchanger 6 to about 540i F.. it is passed through the heating coil 1 at the rate of 25,000 gallons per hour and then through the vertical'soaking drum l in downward direction. The cracking stock is heated in the coil to a' temperature between 900 and 930 F. and a pressure bf between 250A and 1,000 pounds per square inch is maintained on the Isoaking'drum. The

separator is 'under a pressure of 10o-150 pounds lsure oi .95 to 145 pounds per square inch, the

temperature at its top between 40o-450 l". and at its bottom between S-680 F. 'lha distillata mixed product containing gasoline and cycle oil.

ond-meitioned cracking step with the products obtained is approximately 6,550 gallons per hour. 3150 gallons per hour of gas are obtained from which 1315 gallons of gasoline and 1835 gallons per hour of .stripped fuel gas are produced. The cycle stock is submitted to a selective solvent treatment (withrphenol) as a result of' which there is obtained after the removal of the selectivesolvent, 6250 gallons per hour4 of ramnate the presence of a sulfactive catalyst at a temf perature of 750850 F. and a pressure of 3000- 3500 pounds per` square inch. There are obtained 7000 gallons per hour of overhead product separable by distillation into 4500 gallons per hour of 400 F. endpoint gasoline and 2500 gallons per hour of an excellent grade of water white. distillate of 3840 A. P. I. gravity and.. above the boiling range of gasoline. The gasoline o-b. tained is of 56-60 octane number by the Co-operative Fuel Research Motor Method and highly susceptible to improvement of octane number by the addition of tetraethyl lead. Alternatively they 'extract may be subjected to sulfurization or other chemical treatment.

My process may be modified in various ways. Thus,for example, different solvents may be used according to thevmiscibility of the fresh feed with aniline.` In the foregoing specific example the cycle stock subjected to extraction with phenol is such that separation of the rafiinate and the phenol-extract mixture takes place at a temperature above the freezing point of phenol. If the fresh feed'is misclble with aniline at a relatively low temperature and the cycle stock subjected to extraction is completely miscible with phenol at the freezing point of the phenol, then a solvent of lower freezing point such asaniline may be used. By the addition of a seoond storage tanld similar tostorage tank 20, either of the two solvents may be kemployed according to the character of the cycle stock to be subjected to extraction. Y. f

Many other changes and modiiications of myprocess willbe apparent to those skilled in the art and the same is not to be limited by the specic example given for illustration but only by the following claim in which it is my intention to claim all novelty inherent in the invention.

What I claim is: l

'Ihe process of converting a Zas oil .into hydro- 2 carbonsboiling within the gasoline range which comprises subjecting the gas oil to vcracking under conditions suitable for the production of 'a extracting the'cycle oil with a selective solvent for aromatic hydrocarbons whereby a ramnate and an extract are obtained, combining the rafilnate with the initial gas oil to be cracked, subiecting the extract to cracking at a higher temperature than that' maintained in the nrst cracking stepto produce agasoline of high octane number and higher boiling hydrocarbons. and merging. the products of cracking'from'the secofcra'oking Iter."

from the first-mentioned cracking mwaanr. Y

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