US2965559A

US2965559A - Asphalt manufacture

Info

Publication number: US2965559A
Application number: US775454A
Authority: US
Inventors: Gordon A Mclaren
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1958-11-21
Filing date: 1958-11-21
Publication date: 1960-12-20
Anticipated expiration: 1977-12-20

Description

Filed Nv. y21, 1958 Nollv'l'llisla INVENTOR GORDON A. MC LAREN HIS ATTORNEY United States Patent` C) ASPHALT MANUFACTURE Gordon A. McLaren, Edwardsville, Ill., assignor to Shell Oil Company, a corporation of Delaware Filed Nov. 21, 1958, Ser. No. 775,454

4 Claims. (Cl. 208-41) This invention relates to the manufacture of asphalt. Asphaltic products are widely used in road construction as binders and coating materials and for other similar uses.

Straight run residue from crude petroleum distillation is conventionally vacuum flashed to supply a feed stock for catalytic cracking and to furnish an asphalt-containing residuum or pitch. If the ash operation has been suiciently deep the residuum may have a consistency permitting its use as an asphalt product. However, more often than not the residium requires further processing to increase its asphalt content. One method commonly used involves blowing the residuum withair at an elevated temperature, around 425 F. to 500 F., for a period of time, say several hours, to impart the desired consistency to the asphalt material. The increase in the asphalt nature of the residuum during blowing is attributed to a combination of dehydrogenation, condensation and polymerization of the heavy oils of the vacuum flashed material. The length of time and conditions of blowing are selected to supply products of varying consistencies, penetrations, melting points, and other properties. Blown asphalt has been described as having impaired properties compared to non-blown asphalts produced by other methods, e.g. propane deasfphalting and is believed by some in the road construction business to lack proper ductility. Ductility is the measure of asphalts ability to withstand wear; additionally, an asphalt possessing high ductility exhibits particularly strong bonding power.

A typical residual asphalt from conventional vacuum flashing of a Mid-Continent crude contains approximately asphaltenes. It is possible with air blowing of this material to enhance the asphaltene content, but this is achieved at the expense of the heavy oil content of the residuum which, if separated from the asphaltene, would provide an additional, suitable feed stock for cracking. Furthermore, in air blowing there is a loss of a certain amount of material as carbon dioxide, water and low molecular weight materials.

It is an object of this invention to provide an improved process for increasing the asphaltene content of `vacuum ashed residuum. Another object of the invention is to provide `an additional feed stream for cracking and thereby to upgrade a portion of the vacuum ashed residuum to a generally more valuable material. Still another object of this invention is to supply a flexible process for the manufacture of asphalt products of widely varying consistencies without resorting to air blowing. These and other objects will become more apparent with a reading of the following disclosure, taken in conjunction with the drawing which is a schematic representation of a preferred system for the practice of the process of the invention.

It has now been discovered that a straight-run residue from a crude petroleum distillation may be processed to increase its consistency and asphaltene content without resorting to air blowing. In this improved process, the residue from the crude distillation is first subjected to a conventional vacuum flashing to obtain a residuum (pitch) of significantly increased asphalt content. A portion of the asphalcontaining residuum is intimately mixed with a liquid straight-run distillate which has an appreciably lower boiling temperature and a much higher paraffin content than the residuum. The resulting mixture is separated to form an asphaltene-enriched first fraction having a lesser amount of the distillate and a distillate containing second fraction enriched in the nonasphaltene materials of the residuum. The asphaltene containing first fraction is returned to the crude petroleum distillation and there the distillate appearing in this fraction separates from the recycled asphaltene material. It will be seen that this manner of recycling fortiiies the asphaltene content of the crude petroleum residue. The non-recycled portion of the vacuum ashed residuum is continuously removed as the product. In a preferred embodiment of the process, the distillate is stripped from the second fraction and recycled to contact additional quantities of the vacuum flashed residuum. The non-asphaltene material of the second fraction is removed from the stripping zone as a second product and is preferably passed to a cracking operation. This second product can always be used as a charge stock to a thermal cracking unit and can be supplied to a catalytic cracking process providing its metal content is sufciently low. lt is contemplated that 30 to 60% of the recycled residuum (pitch) may be recovered as the non-asphaltene oil (second product).

The distillate employed for mixing with the recycled residuum is most suitably a straight-run gasoline or naphtha and preferably a light straight-run gasoline containing principally C5 to C8 parainic hydrocarbons. Liquid petroleum gas, e.g. propane is not recommended as it may cause a coprecipitation of the heavy resinous oil with the asphaltenes. Additionally, the use of propane would require operation at a relatively low temperature and the use of pressure lines and vessels. For the foregoing reasons, it is advantageous to use somewhat heavier hydrocarbon fractions than liquid petroleum gas for the solvent stripping of the paranic material from the asphaltic constituents. However, the solvent-distillate employed for this purpose should not be too heavy as it would then become uneconomical to separate it from the non-asphaltene portion of the recycled residuum. Consequently, it is recommended that the distillate be a fraction no heavier than light kerosene.

The asphaltene containing residium (pitch) recycle from the vacuum flasher is mixed with a minimum of the solvent distillate, preferably in the range of 2.5 to 7 volumes of the distillate per volume of recyled pitch. In one operation where the crude source is a Mid-Continent petroleum, the recommended solvent-distillate: pitch ratio is 4:1. The maximum ratio will not exceed 15:1. The hardness of the asphalt product can. be controlled by adjusting the amount of recycle. It may be advantageous to operate the process to make a relatively hard grade of asphalt which then may be used as` a blending stock with normal pitch to provide intermediate grades of asphalt. The process admits to exible operations, permitting the production of unblown asphalt of widely varying penetration characteristics and is readily incorporated into existing refinery. Generally, with an increased amount of recycle there is proportionally larger percentage of asphaltene in the asphalt product. A recycle of 30 to 70% of the vacuum tiasher residuum (pitch) normally provides a suitable product. However, it should be realized that the amount of recycle may be widely varied and that the conditions of operation along with the amount of distillate solvent used, are subject to wide adjustments. In processing of a given petroleum crude the amount of recycle used, the ratio of distillate solvent to recycle utilized, the particular distillate solvent employed, time permitted for the separation and settling of the two fractions and other conditions of the process should be properly correlated to the type and to the asphalt content of the crude being processed to produce a productof the desired asphaltene content and to provide a pumpable lower asphaltene-enriched first fraction which may be easily returned to the crude distillation zone. Generally speaking, it is recommended that the lower fraction contain not less than about 50% solvent distillate in order to be readily pumped.

=In the preferred embodiment the recycled residuum and the solvent distillate are mixed under high pressure in a conduit and after thorough agitation are passed to preferably a centrifugation or a filtration. A settling zone may be employed but is not recommended as the lsettling time is usually excessive and the efficiency of separation much less desirable that that obtainable with centrifuging. If settling is to be used for the separation, improvedY results may be had by employing a two or three stage countercurrent system. The second fraction, which contains most of the distillate solvent and which is enriched in the non-asphaltene materials of the recycle residuum, is passed to a fractionating tower of conventional design `where its two components are separated, with the solvent distillate being taken overhead to recycle and the non-asphaltene materials removed in a liquid stream from the bottom of the stripping zone and introduced to a cracking zone or passed to storage. The asphaltene-enriched first fraction, which will also carry a significant proportion of the distillate solvent, is moved to the crude distillation zone and here the solvent distillate separates from the asphaltenes into its appropriate distillate fraction and the recycled asphaltnes are removed from the base of the distillation zone, along with the distillation residue and transferred from there to the vacuum fiasher.

The asphaltene enriched first fraction by being returned first to the crude petroleum distillation is readily stripped of its distillate solvent component. If this fraction were recycled directly to the vacuum flashing zone, by-passing the crude distillation zone, the large quantity of distillate solvent flashed there would interfere with the effective stripping of the straight-run residue itself. Furthermore, straight-run gasoline, the recommended solvent distillate, while it is frequently reformed to enhance its octane rating, is not desirably catalytic cracked with the overhead stream from the Vacuum flashing of a straight-run residue.

EXAMPLE 'leaves the tower via a line 14, a straight-run gasoline stream which is removed through a conduit 16 to a storage tank 17 and draw off

lines

46, 47, 48, 4 9, respectively, lfor liquid petroleum gas., kerosene, light gas oil and heavy gas oil. The heavy gas oil may be passed to catalytic cracking. The straight-run residue flowing in the line 14 in the amount of 42.7 barrels per 100 barrels of crude feed is introduced to a vacuum flasher 18 operating under conventional conditions of about 50 mm. Hg and with a furnace transfer temperature of 800 F. A stream of lighter materials (32.0 barrels) leaves this fractionation operation in an overhead line 19 while a residium (pitch) stream (10.63) bbl.) having an appreciably increased asphaltene content exits from the base of the tower through aline 21. The residue stream 21 is made up of l part asphaltenes and 4 parts of heavy oil. The asphalt product is taken from the line 21 in a product removed line 52. A portion (3.13 bbl.) of the vacuum-flasher residuum is withdrawn in a recycle stream via a line 23 into the inlet of a pressure pump 24. This recycle material is intimately mixed with approximately 4 volumes of unstabilized, untreated gasoline per volume ofrecycle material) supplied in a line 26 under the high pressure of a pump 27. Line 26 is an extension of a gasoline make-up line 40 running from the storage tank '17. The mixing is accomplished in a conduit 29 at a pressure, for example, of approximately p.s.i. gauge. The intimately mixed solvent distillate (gasoline) and recycled residuum are introduced to a large centrifuge 31. Here the more paraffinic portion of the recycled material tends to separate with the solvent distillate (gasoline) into one fraction while the more lcondensed aromatic type material separates into another stream.

The asphaltene-enriched stream is withdrawn from the centrifuge via a line 33 and a pressure pump 35 and is passed to the crude feed line 10. This stream will contain approximately 0.63 barrel of asphaltenes per 0.52 barrel of solvent distillate and 0.11 barrel of heavy oil. The other stream made up principally of the solvent distillate (12.0) bbl.) and the non-asphaltene portion (2.4 bbl.) of the recycled residuum moves via a line 37 to an intermediate section of a fractionation tower 46. This tower is provided `with a suitable number of plates and adequate heat to assure a substantially complete rectification of the two components of the feed. The overhead stream made up almost completely of the straight run gasoline (12.0 bbl.) leaves up almost completely of the straight run gasoline (12.0 bbl.) leaves via a line 42 to the gasoline recycle line 26 and from there is returned to intimate mixing with the recycled residuum. Thel non-asphaltene material (2.4 bbl.) exits from the bottom of the stripping tower 46 through a line 44 and is passed to a cracking zone. The gasoline solvent lost in the stream 33 from the centrifuge is compensated for by the addition of an approximately like quantity to the recycle gasoline via the make-up line 40.

I claim as my invention:

l. In a process for manufacturing an asphalt product from a straight-run asphaltic residue of a crude petroleum distillation, the improvement comprising subjecting the residue to a vacuum flashing to obtain an asphaltic residuum of significantly increased asphaltene content, dividing the asphaltic residuum into a first portion and into a second portion, intimately contacting the first portion which comprises 30 to 70% of the asphaltic residuum with a normally liquid straight-run distillate having an appreciablyrlower boiling temperature and higher paraffin content than the residuum to obtain an asphaltene enriched first fraction containing some of the distillate and a distillate containingY second fraction enriched in the non-asphaltene material of the residuum, returning the asphaltene enriched fraction of the crude petroleum distillation and thereseparating the distillate therefrom, and continuouslyA removing the second portion of the residuum from the vacuum-flashing as product.l

2. A processin accordance with claiml wherein the distillate vis strippedfrom thesec'ond'fraction and recycled 'for-contacting-"further portions of theV residium and the non-asphaltene material of the second fraction is References Cited in the le of this patent l'elllvedr as 8. SeCOnd pl'OdllCt. UNITED STATES PATENTS 3. A process in accordance. with claim 1 wherein the distillate is a straight-run gasoline. 1949989 Bray Mar- 6 1934 4. A process in accordance with claim 1 wherein the 5 2276155 Carr Mar- 10' 1942 distillate s intimately mixed with said first portion of FOREIGN PATENTS the as haltic residuum from the vacuum flashing in the amouiit of 2.5 to 7 volumes of the distillate to one volume 339470 Great Bntam Dec 11' 1930 of the asphaltic residuum.

Claims

1. IN A PROCESS FOR MANUFACTURING AN ASPHALT PRODUCT FROM A STRAIGHT-RUN ASPHALTIC RESIDUE OF A CRUDE PETROLEUM DISTALLATIOIN, THE IMPROVEMENT COMPRISING SUBJECTING THE RESIDUE TO A VACUUM FLASHING TO OBTAIN AN ASPHALTIC RESIDUUM OF SIGNIFICANTLY INCREASED ASPHALTENE CONTENT, DIVIDING THE ASPHALTIC RESIDUM INTO A FIRST PORTION AND INTO A SECOND PORTION, INTIMATELY CONTACTING THE FIRST PORTION WHICH COMPRISES 30 TO 70% OF THE ASPHALTIC RESIDUUM WITH A NORMALLY LIQUID STRAIGHT-RUN DISTILLATE HAVING AN APPRECIABLY LOWER BOILING TEMPERATURE AND HIGHER PARAFFIN CONTENT THAN THE RESIDUUM TO OBTAIN AN ASPHALTENE ENRICHED FIRST FRACTION CONTAINING SOME OF THE DISTILLATE AND A DISTILLATE CONTAINING SECOND FRACTION ENRICHED IN THE NON-ASPHALTENE MATERIAL OF THE RESIDUUM, RETURNING THE ASPHALTENE ENRICHED FRACTION OF THE CRUDE PETROLEUM DISTILLATION AND THERE SEPARATING THE DISTILLATE THEREFROM, AND CONTINUOUSLY REMOVING THE SECOND PORTION OF THE RESIDUUM FROM THE VACUUM FLASHING AS PRODUCT.