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Home | Alpha Telephone | Domain Names | Web Hosting | Get Traffic | xrEvidence | xrSoccer United States Patent
Production of lubricating oils blending stocks The production of normal and premium lube grade blending stocks of 100, 300 and 700 second neutral material along with high boiling by-product material is improved by using a low pressure vacuum tower provided with an overflash separation in the tower bottom from resid.
Attorney, Agent or Firm: What is claimed is: 1. In an operation for the production of a plurality of different lube stocks from a reduced crude and the recovery of higher boiling by-product material, the improvement which comprises processing a reduced crude through a low pressure drop vacuum tower maintained at a pressure below 50 mmHg arranged to separate a plurality of different relatively narrow boiling range lube base fractions from an overflash fraction boiling in an initial portion above 1000.degree.F and a vacuum resid fraction, processing each of said relatively narrow boiling range fractions through a plurality of solvent extraction steps to remove undesired aromatics and wax sufficient to produce normal and premium grade lube blending fractions, processing said overflash fraction admixed with a portion of said resid fractions through propane deasphalting to produce a raffinate phase and an asphalt phase and prcessing the raffinate phase through solvent extraction to produce an improved bright stock. 2. The operation of claim 1 wherein the lube base fractions are passed sequentially through furfural and methylethyl-ketone solvent extraction steps. 3. The operation of claim 2 wherein the different lube base fractions are separated to make a quantity of premium grade lube blending materials and at least the premium grade materials are subjected to hydrofinishing. 4. The operation of claim 1 wherein the recovery of wax and bright stock is improved and the volume of reduced crude charged to the process is significantly reduced to produce a desired volume of products. 5. The operation of claim 1 wherein the vacuum distillation tower is arranged and operated to produce a 100 second neutral fraction and at least one other fraction boiling intermediate said 100 neutral fraction and said overflash fraction. 6. The operation of claim 1 wherein the vacuum distillation tower is arranged and operated to produce a 100 second neutral fraction, a 250 second neutral fraction and another fraction lower boiling than said overflash material. 7. The operation of claim 1 wherein the vacuum distillation tower is operated at a pressure not exceeding about 40 mmHg and the pressure drop therein is less than about 15 mmHg. 8. The operation of claim 1 wherein the vacuum tower is essentially a packed distillation tower. 9. The operation of claim 1 wherein the raffinate product of propane deasphalting is hydrofinished after furfural and methyl-ethyl-ketone solvent extraction. BACKGROUND OF THE INVENTION Lubricating oils of normal and premium grades have been developed over the years for many different applications of severity use including automotive, transformer oils, turbine oils, and heavy cylinder oils. Whatever the use intended, a lubricating oil must be stable, have a high flash point and retain its lubricating properties over an extended operating period. Separation of the crude into base stocks of different viscosities is usually carried out by vacuum distillation followed by separate treatment of each fraction by solvent extraction and sometimes hydrofinishing in specific applications. The facilities relied upon for processing available crudes are dependent upon the quality of the crude processed and the characteristics of the product desired. These considerations have grown in importance as the improvement in quality of product has increased. In the prior art systems large quantities of available crude were processed to prepare desired product. However, with the present scarcity of available crude, it is important to provide a process which will reduce the quantity of crude processed without reducing the quality of product produced. The present invention is directed to such an improved process. SUMMARY OF THE INVENTION This invention relates to the preparation of lubricating oils. In a more particular aspect the present invention is concerned with an improved combination of processing steps for preparing more select lubricating oil blending stocks. More particularly the present invention relates to an improved vacuum tower operation for the separation of more select fractions of lube oil blending components and components for asphalt production. In a particular aspect the present invention is directed to the recovery of 100, 300 and 700 second neutral fractions of a selected boiling range which are more amenable to solvent extraction processes and hydrofinishing thereof under conditions particularly restricting the volume of oil charge required to produce a given volume of desired lube oil blending stocks. DISCUSSION OF SPECIFIC EMBODIMENTS In the combination operation of the present invention comprising vacuum distillation, furfural extraction, methyl ethyl ketone-aromatic extraction and hydrofinishing, it has been found particularly advantageous to rely upon a low pressure drop vacuum distillation tower operation designed to operate at a bottom pressure no higher than 50 mmHg and preferably it is retained at a bottom pressure of about 40 mmHg or lower. More particularly, to improve upon the quality of asphalt producing components, the vacuum tower of the present invention withdraws an overflash fraction from the lower portion of the tower higher boiling than a recovered 700 second neutral fraction, which is passed to a PDA extraction zone with a portion of the remaining vacuum tower bottom residue. By practicing the processing concepts of the present invention it has been determined that the capital investment of the combination is lowered by as much as 10 percent; the utility consumption is lowered by as much as 30 percent; the crude requirements of the process are lowered by as much as 15 percent; the quality of the lube product is improved and more high melting point paraffin wax is obtained by the process. In the combination operation of this invention the vacuum tower relied upon to separate for example Middle East crude into desired lube oil base stocks is maintained at a bottom pressure lower than normally employed heretofore in a packed tower design providing not more than about 15 mmHg pressure drop. The vacuum tower is maintained under conditions providing a flash zone temperature within the range of 690.degree. to 735.degree.F. and a top temperature within the range of 120.degree. to 135.degree.F. The low pressure drop tower design of this invention permits the more select recovery of 100, 300 and 700 second neutral fractions or other fractional variations thereon such as a two mode operation comprising a 250 second neutral or a 450 second neutral fraction along with an overflash fraction as identified in the table below. The vacuum tower design of the present invention is thus novel in design; a low operating pressure in conjunction with low pressure drop preferably less than 15 mmHg obtained preferably by use of essentially a packed column containing very few, if any, distillation plates. The vacuum tower design and method of operation is unique in that it permits the recovery of more select and narrow boiling range fractions processed to the blending stocks desired through solvent extraction and hydrofinishing. Table 1 ______________________________________ Over- % 100"N.degree.F. 300"N..degree.F. 700"N.degree.F. flash.degree.F. ______________________________________ 5 682 800 897 995 10 689 810 914 1010 30 718 833 944 1046 50 737 857 960 1067 70 758 875 982 1104 90 786 905 1015 1164 95 800 915 1029 1198 ______________________________________ The lube oil fractions of Table 1 recovered from the vacuum tower as herein described are then subjected to a sequential treatment of furfural extraction and MEK extraction. Polycyclic materials are undesirable in lubricating oils because of their low viscosity indexes and poor stability. The polycyclic aromatics are removed in the combination of this invention by furfural extraction. The furfural extraction operation shown in block flow arrangement consists of facilities or tower arrangements suitable to contact the oil charge with the selective solvent plus facilities to separate the solvent from extract and raffinate streams. In this operation, the solvent is vaporized and the heat requirements for this purpose are normally high. Therefore any savings which can be obtained in this high cost area greatly contributes to the efficiency of the operation. In the specific operation of the present invention processing more select boiling range fractions of 100, 300 and 700 second neutral fractions, the extraction operating conditions can be refined to a point that considerable savings are realized not only in the quantity of material processed but also in the volumes of solvent required and the heat requirements of the operation. Thus processing the more select and restricted boiling range materials recovered as hereinbefore described avoids solvent overtreating the low boiling component portion of the particular fraction as well as an insufficient solvent treatment of the high boiling components of the fraction. The savings also contribute significantly to equipment savings as mentioned herein. More specifically the furfural extraction of the 100 second neutral fraction may be accomplished with 175 percent volume furfural based on charge at an effective temperature of about 195.degree.F. when maintaining the furfural extraction tower gradient, top/bottom of about 220.degree./180.degree.F. The 300 second neutral fraction may be furfural extracted with 200 percent volume solvent based on charge at an effective temperature of about 205.degree.F. and a tower temperature gradient from top to bottom of about 230.degree./190.degree.F. The 700 second neutral fraction, on the other hand, may be furfural extracted with 225 percent volume solvent based on charge at an effective temperature of about 250.degree. and a tower temperature gradient from top to bottom of about 265.degree./235.degree.F. The relatively narrow cut lube oil fractions herein defined following the removal of undesired polycyclic aromatics are then subjected to a further extraction to accomplish solvent dewaxing with the solvent (MEK) methyl ether ketone-aromatic solvent. The ketone solvent causes wax to solidify into a filterable crystalline form. The aromatic component of the solvent increases the oil dissolving capacity of the solvent. In the MEK (methyl ethyl ketone) extraction operation, the wax bearing oil charge is mixed with the solvent and the mixture is chilled to crystallize the wax. The chilled feed is continuously filtered to recover a wax cake. The MEK dewaxing operation is accomplished at a few degrees below in the range of 5.degree. to 20.degree. below the pour point of the product oil desired. Thus a filtrate comprising oil and solvent is recovered which is then separated to recover a dewaxed oil fraction from the solvent material. In the combination operation of this invention a 50/50 MEK/toluene solvent composition is generally relied upon to accomplish dewaxing of the specific lube oil fractions. This may be varied either way by about 25 vol. percent. The filtration temperature for the 100 second neutral is about -20.degree.F.; for the 300 second neutral about -15.degree.F; and about 5.degree.F. for the 700 second neutral material. The amount of solvent employed in the various steps of MEK solvent dewaxing will vary with each fraction but will be kept to a minimum consistent with obtaining desired results. The overflash fraction recovered from the lower portion of the vacuum tower is combined with a portion of the vacuum resid and passed to propane deasphalting. In a specific example it is contemplated combining, base on crude charge, about 4 volume percent of the overflash with a portion of the vacuum resid varying from about 10 to 60 volume percent as feed to a PDA (propane deasphalting unit). Bright stock viscosities may be varied by varying the amount of resid passed to the PDA unit. In the PDA unit the above defined mixture is treated with propane solvent near its critical temperature which dissolves the hydrocarbon phase and rejects the asphaltic materials. In the combination of this invention, this separation is enhanced by the recovery of overflash material which is combined with a desired portion of the resid withdrawn from the bottom of the vacuum tower. In the range of conditions used in the PDA operation such as 100.degree. to 150.degree.F. in the bottom and from 150.degree.F. to 180.degree.F. at the top of the tower, raising the temperature of the propane reduces its dissolving capacity but improves its selectivity. On the other hand, increasing the propane to oil ratio further increases the separation sharpness. The operating pressure is sufficient to retain the propane in liquid phase. The heavy oil product of PDA treatment is thereafter subjected to furfural and MEK treatment under conditions particularly selected to retain the oil product in substantially maximum yields. The drawing is a schematic arrangement in block flow representing the processing combination of the present invention. In the arrangement of the drawing, a crude oil charge is introduced by conduit 2 to a vacuum distillation column 4 maintained at a bottom pressure of about 40 mmHg. The tower 4 is primarily a packed volumn arranged for about 15 mmHg pressure drop. The vacuum tower is operated under conditions selected to produce the fractions identified in Table 1 above along with a gas oil fraction withdrawn from an upper portion of the tower by conduit 6 and a resid material withdrawn from the bottom of the tower by conduit 8. In a specific operation, the gas oil fraction amounts to about 10 vol.% of the charge and the resid is about 11.5 vol.% of the charge. A 100 second neutral fraction is withdrawn by conduit 10 and amounts to about 8.6 vol.% of the charge. Any excess of this material over that desired to be processed may be withdrawn by conduit 12. A 300 second neutral oil fraction amounting to about 7.5 vol.% of the charge is withdrawn by conduit 14 and separated into stream 16 for use in preparing normal oil blending stock and stream 18 for use in preparing premium oil blending stocks. An overflash boiling range material identified in Table 1 and amounting to about 4.0 volume % of the feed is withdrawn from a lower portion of the vacuum tower above the charge inlet by conduit 26. A portion of the vacuum tower resid withdrawn by conduit 8 is withdrawn by conduit 28 and combined with overflash material in conduit 26 before passage by conduit 30 to a PDA unit 32. In the PDA unit, the blend of overflash with resid and operating conditions relied upon are such as to provide an oil product comprising about 48.8 vol.% of the charge thereto which oil product is withdrawn therefrom by conduit 34. An asphalt product of the precess is withdrawn by conduit 36. The heavy oil product in conduit 34 is thereafter subjected to furfural extraction conditions for the removal of polycyclic material thereby providing a product therefrom amounting to approximately 68 vol.% of the oil stream charged thereto. The raffinate-oil product of extraction is then passed by conduit 38 to solvent dewaxing accomplished with a MEK/toluene solvent mixture. In this operation the conditions are selected to recover about 77 vol.% of the feed as a dewaxed oily product. The dewaxed oil is then passed by conduit 40 to a hydrofinishing operation wherein it is contacted with a hydrofinishing catalyst at a temperature within the range of 400.degree. to 700.degree.F. (prefer 450.degree.F. to about 550.degree.F.) and a pressure selected from within the range of 200 to 600 psig. In a specific operation a 95VI heavy lube oil bright stock in conduit 40 is hydrofinished to a color lighter than 5 ASTM. This product material will normally boil above about 900.degree.F. and is withdrawn by conduit 42. The 700 second neutral oil fraction in conduits 22 and 24 are passed to furfural extraction for the removal of polycyclic materials under conditions permitting the recovery of about 55 vol.% of the oil charge in conduit 22 by conduit 44 and about 45 vol.% of the oil charge in conduit 24 by conduit 46. The raffinate phase of furfural extraction recovered by conduits 44 and 46 are then passed to solvent dewaxing with MEK as herein described. In the solvent dewaxing operation the conditions are selected to permit the recovery of an oil product amounting to about 77 vol.% of the charge in conduit 44 by conduit 48 and about 66 vol.% the charge in conduit 46 by conduit 50. The oil product in conduit 48 prepared from 700 second neutral material will be about a normal 97 VI dewaxed material. This material produced for use as normal blending stock may be subjected to hydrofinishing conditions if desired. The premium oil blending stock recovered by conduit 50 is subjected to hydrofinishing temperature conditions and catalyst contact selected to improve the quality of this material suitable for use as premium blending stock. In this specific arrangement a 100 VI dewaxed material is produced and will be withdrawn from the hydrofinishing operation by conduit 52. The 300 second neutral material recovered from vacuum distillation is passed by conduit 16 and 18 to furfural extraction operation particularly designed to produce a normal oil product recovered by conduit 54 and a premium oil product recovered by conduit 56. The normal oil furfural raffinate amounts to about 55 vol.% of the oil charge and the premium oil raffinate amounts to about 45 vol.% of the oil charged. The raffinate streams in conduits 54 and 56 are then subjected to solvent dewaxing by MEK to produce dewaxed oil product recovered by conduit 58 and premium oil by conduit 60. The normal oil in conduit 58 may be hydrofinished if desired. This material will be about a 104 VI dewaxed material. The premium oil raffinate in conduit 60 is subjected to hydrofinishing conditions to remove aromatics and produce a stable turbine oil product. The hydrofinished premium oil is recovered by conduit 62 as a 108 VI dewaxed material (300 second neutral) for blending purposes. The 100 second neutral oil fraction recovered from the vacuum tower by conduit 10 is subjected to furfural extraction. A raffinate fraction amounting to about 54 vol.% of the 100 neutral charge is recovered by conduit 64 and separated into two streams 66 and 68. Each of the oil streams in conduits 66 and 68 are subjected to solvent dewaxing by MEK. In this operation about 78 vol.% of the oil charge in conduit 66 is recovered as a dewaxed oil in conduit 70 and about 83 vol.% of the charge in conduit 68 is recovered as a dewaxed premium oil blending component by conduit 72. The dewaxed (100 neutral) oil product recovered by conduit 70 is about a 106 VI material. The premium oil in conduit 72 is subject to hydrofinishing conditions to stabilize the oil before it is recovered by conduit 74 as a 110 VI dewaxed material. In the combination operation herein described, a combined extract phase is recovered as by conduit 76 and a combined wax phase is recovered by means represented by conduit 78. To simplify understanding of the complex processing arrangement of the present invention relying upon known processing technology, the various furfural extraction steps, MEK solvent dewaxing steps and hydrofinishing step have been simply identified by rectangular block. It is to be understood however that because of the particularly improved vacuum fractions recovered and subsequently treated, that the overall processing combination reaps significant advantages as herein identified. More particularly, it has been found that by practicing the processing concepts of this invention that as much as 3000 barrels of crude oil can be saved over prior processing techniques for producing the equivalent amount of desired product blending stock. For example, when charging 15469 (BCD) barrels per calender day, of reduced crude to the improved vacuum tower design and operation of this invention, the following product distribution may be obtained as identified in Table 2 below. Table 2 ______________________________________ 100"Normal 521 BCD 100"Premium 14 BCD 300"Normal 849 BCD 300"Premium 239 BCD 700"Normal 348 BCD 700"Premium 259 BCD 150"Base Stock 770 BCD Asphalt 1472 BCD Furfural Extract 2875 BCD Slack Wax 920 BCD Refinery Fuel and Gas Oil Prod. 6802 BCD ______________________________________ An important auxiliary benefit of practicing the processing concepts of the present invention is the production of more select components for asphalt production. More particularly, a full range of paving and industrial asphalts can be formulated from lube byproducts by either direct blending and blending followed by oxidation. In a particular aspect, asphalt penetration grades 65, 90 and 200 have been formulated from blends of some or all of the following lube streams (consult block flow drawing) vacuum tower resid (stream 8), vacuum tower overflash (stream 26), PD asphalt (stream 36), and furfural extracts (stream 76). The ability to formulate asphalt from lube byproducts is a valuable adjunct to the present invention for the following reasons: (1) the cost of transporting, storing and processing special asphaltic crude on a blocked out refining operation is eliminated, (2) the lube byproducts are upgraded from fuel oil to asphalt value, (3) the downgrading of 300.degree. to 500.degree.F. kerosine which must be blended with several of these high viscosity lube byproduct streams to meet fuel oil specifications is eliminated. By selective blending alone or selective blending followed by oxidation of these byproduct streams, asphalts of highly superior quality can be produced. For example, a 90 penetration grade asphalt may be prepared by a selective blending plus oxidation of vacuum tower resid, vacuum tower overflash, and PD asphalt to provide the following properties: Viscosity, CS at 158.degree.F. 485 Penetration (77/100/5) 86 Vis-Pen 41,700 Softening Point, .degree.F. 113 Rotating Thin Film Oxidation Ductility at 59.degree.F. 85 1/16" Thin Film Oxidation Ductility at 77.degree.F. > 140 Having thus generally described the invention and discussed specific embodiments going to the very essence thereof, it is to be understood that no undue restrictions are to be imposed by reason thereof except as defined by the following claims. For U.S. patent law, rules, and procedures see MPEP. Disclaimer. Information presented on this page while believed to be reliable, is provided "as is" with no warranties of its accuracy or timeliness. For legal advice seek help of a licensed professional. |