US2850436A - Method for the preparation of solid petroleum pitch - Google Patents

Description

Sept. 2, 1958 H. BEUTHER ET AL 2,850,436

METHOD FOR THE PREPARATION oF SOLID PETROLEUM FITCH 2 Sheets-Sheet l Filed March 16, 1954 Nm. NN

Sept. 2, 1958 H. BEUTHER ETAL 2,350,436

METHOD FOR THE PREPARATION OE sOLTO PETROLEUM PTTOH Filed March 16, 1954 2 Sheets-Sheet 2 200 25o aan 35o `ma l 2f/m@ 0o/m17( ,90% 75 niteci States Patent 'a hun! IVIETHOD FOR THE PREPARATION OF SOLID PETRLEUb/l FITCH Harold Beuther and Richard G. Goldthwait, Penn Township, Allegheny County, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware Application March 16, 1954, Serial No. 416,634

S Claims. (Cl. 19o-50) This invention relates to a process for the preparation of solid pitches from petroleum crude oils and more particularly to a process of excellent operability for the preparation of solid petroleum pitches having very high softening points and especially suitable for use as solid fuels.

The demand for distillate products from petroleum, notably for gasoline and domestic fuel oils, has increased tremendously during recent years and has made it necessary to reiine increased quantities of crude oils. There has not, however, been a corresponding increase in the demand for heavy residual fuel oils. As a result of this unbalanced demand, the disposal of residual fuel oils at a prot has become increasingly diflicult. At the present time, residual fuel oils, commonly designated as No. 6 fuel oil, are generally sold at a lower price than the crude oil from which they are derived.

Several methods have been employed to increase the percentage of distillate oils obtained from the crude oils. Deeper and deeper cuts have been made into the crude by vacuum distillation to increase the amount of distillate oil available for use as a catalytic cracking charge stock. The increase in distillate oils obtained by this method is limited. If still deeper cuts in the crude oil are attempted, in many instances the distillate is contaminated with metals and has a high carbon residue which makes it unsuitable for use as a catalytic cracking charge stock. In addition, the residual oil obtained from many deeper vacuum reductions is of such a high viscosity that it must be cut with a lighter oil, commonly designated as a cutter oil to produce a salable No. 6 fuel oil. The cutter oil, which is usually a catalytic furnace oil, in most instances could be used in a domestic furnace oil and its blending with the highly viscous residual oils seriously reduces its value.

Another process that has been employed to eliminate the unbalanced demand for distillate and residual oils is the delayed coking process in which no residual oil is produced. This process requires multiple coking drums, expensive `controls and piping, and coke removal equipment. Since it is necessary to place one of the coking drums oifstream periodically to remove coke, the process is expensive to operate. Moreover, the distillate oils obtained in the delayed coking process are cracked oils which are not as good charge stocks for catalytic cracking operations as virgin distillate oils or distillate oils which have only been lightly cracked.

Another possible method of increasing the ratio of distillate oils to residual oils produced in a renery is to produce solid petroleum pitches from some of the residual oils. These pitches, unlike petroleum coke, are liquid at the operating temperatures employed and are therefore removed from the unit as a liquid. This eliminates the need of multiple reactors, as in delayed coking, which must be periodically shut down to remove coke. While the pitches are solid materials, they will flow and fuse Y Patented Sept. 2, 1958 ice or cake when subjected to continued pressure, even at vtemperatures well below their melting point.

Since extremely large amounts of pitches would be produced if a substantial part of the residual oils were converted to the production of pitches, it is probable that the most important use of the pitches would be as a solid fuel. It is essential, therefore, that the pitches be capable of withstanding the pressures and temperatures likely to be encountered when stored in large piles without caking. It Vhas been found that pitches having softening points, as determined by the ring and ball test method (ASTM D36), above about 350 F. may be stored without danger .of caking in piles of heights ordinarily used for storing solid fuels at temperatures normally encountered. On the other hand, pitches having softening points below about 325 F. will cake or fuse when stored in high piles at temperatures of approximately to 130 F., which are likely to be encountered.

The preparation of petroleum pitches of low softening point, for example softening points below about 300 F., has offered no serious diiiiculties. In general, such low softening point pitches may be prepared from any crude oil by processes having satisfactory operability characteristics. However, petroleum pitches having softening points below about 300 F. are not satisfactory for use as solid fuels in many instances because of their poor storage characteristics. The preparation ofpitches having softening points above about 350 F. is far more difficult. Processes employing extremely deep vacuum reductions are costly because of the very large steam requirements. Processes employing severe visbreaking or deep atmospheric flashing with steam generally have pooroperability characteristics.

The term operability is used to designate the ability of a process to continue operation for long periods without shut-downs for cleaning fouled equipment. An indication of the operability of a process in which high boiling residual products are formed is theV amount of insoluble carbonaceous sediment in the residual product. If the sediment is high, operating diihculties resulting from fouling of the process equipment may be expected. Usually, the operability of a process may be improved by reducing the severity of high temperature operations, such as cracking or flashing, in the process, and particularly the time the hydrocarbons are subjected to high temperatures.

This invention resides in the preparation of petroleum pitches having softening points of approximately 350 F. or higher by visbreaking a residue containing at least about thirty percent asphaltenes and having a softening point of F. or higher. The visbroken residue is then flashed at a temperature which is suiciently low to avoid cracking in the flash tower to produce a pitch of the desired softening point as a bottoms product.

Figure l is a diagrammatic ow sheet of the process for the preparation of petroleum pitches according to this invention.

Figure 2 is a plot showing the relationship of the fusion temperature of the petroleum pitches under simulated storage conditions to the ring and ball softening point of the pitches.

. The data from which Figure 2 of the drawings was preparedwere obtained by subjecting pitch of the indicated softening point to a pressure corresponding to the pressure exerted by a pile of the pitch forty feet high for a period of twenty-four hours. The fusion temperature is the temperature at which the pitch caked when stored under pressure for the test period. The data set forthV in Figure 2 of the drawings were obtained for a petroleum pitch prepared from a Baxterville (Mississippi) crude. The fusion temperature for pitches prepared from that apetroleum pitch having a softening pointof Yarp-V proximat'ely 350 F. fusesrat a temperaturefslightlyabove 140 F. VIn addition to their good Ystoring qualities, petroleu'mpitches having softening points in excess of about 350',F. are brittlerand easily pulverized to form apowdered f uel.V `lOnthe other hand, if the softening point of-thepitch is approximately 300 F., it will fusey under thetest conditions at a; temperature of approximatelyY 100 Temperatures higher than 100 F. and up to aboutV 130 Fjniay frequently exist in storage piles either because of heat from the direct sunlight and the surrounding atmosphere, or because of the pitch being warm when piled. Y Y

The petroleum pitches of approximately 350V F. and higher, and not less than 325 F., `softening point 'are prepared according to this invention from residues ofY certain crude oils. The crude oils providing suitable sources 'of the residues are any crudes `from which resi-V dueshaving softening points, as determined by the ring and ball method, above 160 F. andan asphalt'ene contentabove thirty percent may be derived. In` general,

thepreferred crudes are those usually describedV as.

asphaltic base crudes, such as those from Baxterville, Merey, and'Eastern Venezuela elds.

ern'Venezuela, and heavy Eastern Venezuela crudesg The designation fheavy ordinarily indicates that the crude has a gravity of about 20 API or lower; however, gravity alone doesnot determine whether or not a crude oil is ay satisfactory chargeV stock Vfor Ythe preparationl of the.

pitches. The composition Vof lthe highest boiling point fractions of the crude oil rather than thecomposition of the entire crude 'determines whether or not the crude will be asatisfactory charge stock. ,l Vf The crude oils are passed through an atmospheric dis- Ytillation unit inwhich gases, gasoline, and 'light gas oilY are separatedfrom the Vbottoms which are passed to a vacuum distillation unit. ".The atmospheric distillation is a conventional operation in which the fractions separated as separate streams will be determined by the crude oilr processed andthe requirements of the refinery. The` vacuum distillation is a deep reductionof the bottoms from the atmospheric distillation, but presents no serious operational diculties. For example, a vacuum distilla- Y Other preferred crudes are those designated as heavy Mara,rheavy Westtion at a ash temperature of 1030 F., corrected to 760 mm. of mercury pressure, may be employed. VThe vacuum reduction of the crude oil removes heavy oils fromV the residue. lThose heavy oils are virgin distillates which are desirable as charge stock for catalytic cracking. The vacuum reduction must be sufciently deep to provide a residuek having a ring and ball softening point" above 160 F. and an asphaltenev content above about thirty percent for use as a charge stock to subsequent operations. The asphaltene content may be determined by dissolving a known weight of the residue in approximately ten timesV its volume of pentane, separating the solubleV and insoluble material, washing the insoluble material with additional pentane until a residue of substantially constant vweight is obtained, removing pentane from the residue, and weighing the residue'. The asphaltene con-j tent is expressed in terms of the percentage of the original f a petroleum pitch offthe desired softening point 2,850,436 Y Y f through coil cracking operation and about fteen percent or less of the charge to the visbreaking operation is'converted to gasoline of 400 F. end point. The time of cracking is indicated Vby, a coil volume of approximately 0.012 to 0.050 cubic foot above V750" F. per barrel throughput per day. In' some instances, it is desirable to quenchthe products discharged from theV cracking operation with steam, naphtha, gasoline, light gasoil, etc. to reduce and control the temperature to prevent further cracking,- t

The visbroken residue is then .ashed in atower, operated preferably. at substantially atmospheric pressure and Y at temperatures snliciently low `to prevent further ycracking ofthe heavy oils, to produce a pitch of the desiredV softening point. point and lighter products is not a complete indication of the Voperability of the process. lf the temperature of the atmospheric ii'ash tower is sufficiently high V:for cracking to occur therein, (the relatively long residence periods of liquids and vaporized heavy oils in the tower will, re-Y sult in'excessive Vcoke formation and foulingk ofthe tower. Excessive coke formation in the flash tower isrprevented; by maintaining Vthe tower at ya temperature not exceeding 810 VVF. Vln some instances it is` desirabler to add steamn tothe Vhash tower to aid` in stripping high boiling point oilsfrom the pitch; The 'amount of steam added'willn depend upon many factors among which are the crude beingprocessed, the cracking severity in the visbreaking coil, the temperature of the ilash chamber, the stripping eiciencyofthe apparatus and the desired softening'point ofthe pitch. The amount of steamemployed may 'range from10`to 80 pounds per barrel o f `charge to the visbreaking furnace. Steam,rgases, gasoline, andgas oil are delivered overheadfrom the atmospheric flash towerV and is with? drawn. as a bottoms product. A

. The pitch `produced 'by this invention in addition to hav-1V ing'a finite ring and ball softening pointof abou-t 350fF.

-and higher 'hasa specific gravity usually ranging fromV 1.050 to 1.175 yand. not exceeding about l.200.` The specific gravity of thepitch isan indication in part ofithef amount Vofcrackingof the residue. Specific gravitiesfin` excess'ofr-1;200"are1 an Vindication that the pitch has been severely Icracked either in the visbreaking furnaceor the.

subsequentash distillation. The pitch is vcharacterized` by being substantially Lcompletely soluble in trichloroethylene' or carbon disnlde, having a'penetration.below?y 5 at 210"v F1100 grams/ 5 seconds Aand a 'hea-t of combustion of Vabout V17,000 B. t. u.s perpound.

An embodiment of apparatus suitable for the preparation; of petroleum pitch according to this inventionzis: illustrated'diagrammatically in Figure 1. A petroleum Y crude oil of the type described above is introduced through lineY llljinto an atmospheric distillation tower 12. Light gas `oil `and more volatile fractions are withdrawn from tower 12 as distillate products or through suitableside. draw-olf lines,V such as .lines 14.and.16, and an overhead, product Iline, 18. A heavy bottoms product is withdrawn from the bottom of the 'atmospheric distillation tower 124 through line 20 and dischargedinto a vacuum distillationtower 22. A heavy gas oil suitable for charge stockV tov a catalytic ycracking operation is distilled froml tl'ietopV of -tovver22v through line 24u and Vaheavy residual oil suitable forV the preparation of petroleum pitches according` toi'this invention V'is withdrawn from the 'bottom vof'V vacuum tower 22 through `aflin'e26-i The atmospheric distillation tower 12 4and vacuum Y tower 22 are conventional apparatus for theproce's'sing.

ofrpetroleum oils and Vother suitable apparatusmay `beY substituted for those towers. It is essential ',to this invention, however, that the residual oil withdrawn through 1 ine-26r have a ringand ball softening point 'higherthan F. 'and "containat least Vabout thirty percent asphaltenes. Y Y A pump 28 increases the pressure onY theresidual oil The totalY conversionv to 400"F. end Y gna . 9 in line 26 to `a pressure suitable for visbreaking and pumps the residual oil through heating coils 30 in a visbreaking furnace 32. The temperature of the residual oil is increased to a temperature f 900 to 950 F. in the furnace 32. Visbreaking furnace 32 is operatedto crack the residual oil in a short-time operation at relatively high temperature. The conversion to 400 F. end point gasoline does not exceed approximately fifteen percent of the residual oil.

The euent from the visbreaking furnace is delivered through a line 34 and a pressure reducing valve 35 into -an atmospheric flash tower 36 in which cracked heavy gas oil and lighter fractions are distilled overhead. Vaporization of the overhead products from the flash -tower 36 may be aided by the introduction of steam through a line 38. The petroleum pitches of this invention are withdrawn from the bottom of the tower 36 and delivered to storage through a line 40.

The distillate from atmospheric flash tower 36 is delivered overhead through a line 42 to an atmospheric dis- -tillation tower 44. Distillation tower 44 is of conventional design and operation for the separation of the lower boiling fractions from a heavy bottoms oil, ondinarily used in No. 6 fuel oil, which is withdrawn from the tower 44 through the line 45. In the distillation tower 44 illustrated in the drawings, side streams of gasoline, naphtha and gas oil are withdrawn through lines 48, 50, `and 52, respectively, and gas is taken off overhead through a line 54.

In order to control the temperature of the material discharged from the visbreaking furnace 32 to prevent further cracking, a quench stream may be introduced into line 34 through line 56. The quench `stream may be of steam, naphtha, gasoline, or gas oil. In the flow sheet illustrated in Figure l of the drawings, a recycle line 58 is provided to return a quench stream from the distillation tower 44 to line S6 and then into line 34.

Petroleum pitches were prepared according to -this invention from the residues of several crudes. The results of the runs for the production of petroleum pitches are set forth in the following table.

following the visbreaking, even though the residue consti'- tutes a long cut of the crude.

The softening point of the residue charged to the visbreaker is of extreme importance in determining the softening point of the pitch obtained. A comparison of run No. 2 and run No. 5 shows that Yan increase in the softening point of the residue of an Eastern Venezuela crude from 166 to 180 F. results in an increase in the softening point of the resultant petroleum pitch even though the steam introduced into the atmospheric distillatio-n tower was reduced from 79.9 to 43.7 pounds per barrel of charge. Both residues were visbroken at the same temperature prior to the ash distillation. The softening point of the residue charged to the visbreaker is additionally important to the opera'bility of the process. If lower softening point residues are charged to the visbreaker, the amount of heavy oil introduced into the atmospheric ash tower is increased. A pitch of the desired softening point can then be obtained either by markedly increasing the temperature of the atmospheric ash distillation which results in the formation of coke in the ash tower or by increasing the steam rate which may be limited by the design of the equipment.

The softening point of the pitch also depends upon the severity of the visbreaking. For example, it will be noted from run No. 2 and run No. 3 that increasing the visbreaking temperature of an Eastern Venezuela residue having a softening point of 180 F. from 925 to 940 F. allows a reduction in the steam required in the flash tower from 44 pounds per barrel of charge to 0 without appreciahly reducing the softening point of the pitch.

The softening point of the pitch is also determined by the temperature and steam rate employed in the atmospheric flash distillation of the visbroken residue. In the examples set forth in the table, the temperature in the flash tower was substantially constant in all runs with the exception of the run in which residues from Baxter- Ville and Merey crudes were the charge stocks. The steam introduced into the flash tower is then a measure of the effect of increased severity of flash conditions. As shown by runs Nos. 3 and 4, an increase in the steam TABLE I Production of pitch by vsbreakng of vacuum reduced crudes Crude oil source West. East. Mara, Bax- Ku- EasternVenezuela Ven., Ven., hvy. terwait* Merey hvy. hvy. ville Run No 1 2 3 4 5 6 7 8 9 10 11 Charge stock, percent of crude.-." 9. 7 11.6 11.6 1l. 12.6 46. 2 37. 2 48. 8 33.3 14. 4 26.1 Grav1ty,APr 3.8 5.2 5.2 5.2 5.2 3.6 3.0 2.9 0.8 2.4 0.4 softening po1nt,F 218 180 180 180 156 162 182 195 280 105 245 Asphaltene content, weight percent 38.9 32.4 32.4 32.4 29.8 27.2 33.7 38.7 54.4 28.8 48.6 Operating conditions:

Furnace temp,F 925 925 940 940 925 940 925 925 925 900 925 Furnace pressnre,p.s.1.g 200 200 200 200 200 200 200 200 200 200 200 Furnace coil vol. above 750 F., en. ft./bb1./day 0.020 0.020 0.020 0.020 0.020 0.020 0.020 0.020 0.020 0.020 0.020 F1ashtemp.,r 806 800 809 806 803 795 800 800 775 800 775 Stripping steam, lb./bbl. of

charge 0.0 43.7 0.0 17.9 79.9 20.8 37.1 31.9 0.0 53.8 0.0

Pitch properties:

Specific gravity solid state, 77

F.77F 1.120 1.154 1.143 1.178 1.095 1.213 1.161 1.167 1. 035 1.212 1.1 softening po1nt,F 347 364 360 380 345 361 357 334 392 35e 350 Propane asphalt.

It will be noted from the data presented in the above introduced into the ash tower from 0 to 17.9 pounds table `that the softening point of the pitch will depend per barrel of charge resulted in an lncrease of 20 F. to an important extent upon the crude oil from which the in the softening point of the pitch, even though the charge stock to the Visbreaking operation was derived. residue charged to the visbreaker and the visbreakmg For example, pitches having softening points above 350 conditions were the same in both mstances.

F. may be prepared from Baxterville and Merey crudes This invention has been descr1bed for the preparation with visbreaking temperatures of 925 F. without the 75 of pitches by visbreaking residues obtalned by d1st1llaaddition of steam in the atmospheric ash distillation tion of certain crudes. Residues obtained by other

Claims (1)

1. A PROCESS FOR THE PREPARATION OF A PETROLEUM PITCH HAVING A RING AND BALL SOFTENING POINT ABOVE ABOUT 350* F., A SPECIFIC GRAVITY BELOW ABOUT 1.200 AND SUBSTANTIALLY COMPLETE SOLUBILITY IN TRICHLOROETHYLENE AND CARBON DISULFIDE COMPRISING REDUCING AN ASPHALTIC BASE PETROLEUM CRUDE OIL TO FORM A RESIDUE HAVING AN ASPHALTENE CONTENT ABOVE ABOUT THIRTY PERCENT AND A SOFTENING POINT ABOVE ABOUT 160*F., SEVERLY VISBREAKING THE RESIDUE IN A ONCETHROUGH SHORT-TIME COIL OPERATION AT A TEMPERATURE OF 900* TO 950*F., QUENCHING THE VISBROKEN MATERIAL AS IT IS DISCHARGED FROM THE VISBREAKING COIL, AND FLASHING THE VISBROKEN RESIDUE AT SUBSTANTIALLY ATMOSPHERIC PRESSURE AT A TEMPERATURE NOT EXCEEDING 810*F. TO FROM THE PETROLEUM PITCH AS A BOTTOMS PRODUCT.

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