US3322667A - Hydrocarbon stripping process - Google Patents

Description

3U, i967 s. D. LAWSON 3,322,667

HYDROGARBON STRIPPING PROCESS Filed May 11, 1964 RAF'FINATE 10 JSTRIPPER VAPOR ONE TDEWAXING PROCESS 22 RAFF lNATE Q LIQUID PROPANE INVENTOR. S. D. LAWSON A TTORNEKS 3,322,667 HYDROCARBON STRIPPING PROCESS Shelby ll). Lawson, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware lFiled May 11, 1964, Ser. No. 366,581 8 "Claims. (Cl. 208356) This invention relates to a process for steam stripping a hydrocarbon. In another aspect, this invention relate to a process for separating a solvent from a hydrocarbon. In yet another aspect, this invention relates to an improved process for the production of hydrocarbon lubricating oils utilizing a solvent extraction process step followed by a solvent dewaxing process step.

It is known in the art to produce lubricating oils by various processes comprising distillation, solvent extraction, dewaxing process steps, and the like. In general, three types of hydrocarbons are to be found in the lubricating oil fraction of a crude petroleum, namely, paraffinic, aromatic, and naphthenic hydrocarbons. It is known that the paraflinic type of hydrocarbons have the highest viscosity indices whereas naphthenic and aromatic type hydrocarbons have materially lower viscosity indices. As a result of this, it is desirable that the product lubricating oil contain high concentrations of paraffinic type hydrocarbons and minimum concentrations of naphthenic and aromatic type hydrocarbons.

In order to produce lubricating oils having high concentrations of paraffinic type hydrocarbons, lubricating oil fractions of a crude petroleum are subjected to a solvent extraction process wherein the lubricating oil fraction is contacted with a solvent selective to the removal of the aromatic type hydrocarbon compounds. The solvents conventionally employed for the removal of the aromatic type compounds are less selective for removing naphthenic constituents.

When, for example, phenol or phenol containing a low concentration of water is employed as the selective solvent, the rafiinate phase comprising the paraflinic hydrocarbon fraction is passed to a stripping zone wherein small concentrations of phenol withdrawn from the extraction zone with the raifinate is steam stripped from the raflinate. The steam stripped raflinate is passed to a dewaxing zone wherein high pour point waxy materials are separated from the rafiinate.

A conventional process for dewaxing the raflinate obtained from the solvent extraction step comprises reducing the temperature of the raflinate at a controlled rate to precipitate the wax crystals by the evaporation of a light hydrocarbon such as propane. During the chilling process, the wax crystals form and remain suspended in the propane-oil solution. The chilled slurry is then charged to a filter for separation of the formed wax crystals from the oil.

The steam stripped raffinate passed to the dewaxing process step conventionally contains water which interferes with the dewaxing step, forming ice crystals during the chilling step. To prevent the formation of ice crystals in the dewaxing process, resulting in a substantial reduction in filter efliciency and operation of other dewaxing equipment, it is necessary that water contained in the raffinate feed to the dewaxed process be removed.

Accordingly, an object of my invention is to provide an improved process for steam stripping a hydrocarbon.

Another object of my invention is to provide an improved process for stripping solvent from a hydrocarbon.

Another object of my invention is to provide a process for the separation of water in the hydrocarbon feed to a dewaxing process.

Other objects, advantages and features of my invention will be readily apparent to those skilled in the art from 3,322,667 Patented May 30, 1967 the following description, the drawing and appended claims.

By my invention, I have provided a process wherein a hydrocarbon is steam stripped and the steam stripped hydrocarbon contacted with a vaporous drying agent. Preferably, although not to be limited thereto, the steam stripping and drying steps are conducted in the same vessel.

The invention is applicable to the separation of liquids from hydrocarbons wherein said liquids are more readily volatilized in the presence of steam than said hydrocarbons. Although not to be limited thereto, the invention is particularly applicable to the separation of solvents such as phenol and furfural from hydrocarbon lubricating oil fractions.

The vaporous drying agents employed in the process of my invention are those more volatile than the hydrocarbon feed to the drying zone and preferably more readily volatilized than water. In a process wherein a hydrocarbon is solvent extracted and subjected to a subsequent process step, such as a dewaxing process wherein the said hydrocarbon is contacted with an agent more readily volatilized than said hydrocarbon, it is preferred that the vaporous drying agent employed in the drying step be the same agent employed in the subsequent process step. Agents employed in hydrocarbon dewaxing processes and found to be suitable as vaporous drying agents include butane, propane, methyl ethyl ketone, a mixture of ketones, and a mixture of methyl ethyl ketone and toluene.

Although not to be limited thereto, the invention will hereinafter be described as applied to a raffinate obtained from a phenol solvent extraction process, said raffinate to be subjected to a subsequent dewaxing process. It will be understood by those skilled in the art that the invention is applicable to hydrocarbons withdrawn from other solvent extraction zones such as a furfural extraction zone. The term raffinate as herein employed refers to a lubricating oil fraction that has had the aromatics removed therefrom and contains high pour point waxy materials. It will also be understood by those skilled in the art that the inventive stripping process can be applied to the extract obtained from the phenol solvent extraction process as well as to hydrocarbons in general.

The drawing is a schematic representation of one em-' bodiment of the invention.

Although not to be limited thereto, in the stripping of phenol from a hydrocarbon ratlinate, the weight ratio of stripping steam to hydrocarbon feed is maintained generally in the range of 1:150 to 1:500. Temperatures and pressures in the solvent stripping region of the stripping zone are normally maintained in the range of 350 F. to 700 F., and 10 p.s.i.a. to 20 p.s.i.a., respectively. The weight ratio of propane, when employed, to hydrocarbon in the drying region of the stripping zone is generally maintained in the range of 1:500 to 112000. Temperatures and pressures in the drying region are generally maintained in the range of 350 F. to 700 F., and 10 p.s.i.a. to 20 p.s.i.a., respectively. The stripping tower may or may not be reboiled. Usually the oil is charged at sufiicient temperature that no additional heating is required.

Referring to the drawing, a rafiinate having a viscosity of SSU at 210 F. and containing phenol and obtained from the phenol solvent extraction of a lubricating oil hydrocarbon fraction is passed via conduit means 11 to the top tray of a 24- tray stripper 10 at the rate of barrels per hour.

A mixture of Ellenberger and Burbank crude oils was subjected to atmospheric distillation to produce a topped crude. This topped crude was subjected to vacuum distillation to produce distillates of a gas oil, a 10 raw, and a 20 raw lubricating oil base stock. The vacuum reduced crude was subjected to propane deasphalting, producing a 50 raw and a 250 raw lubricating oil base stock. These raw stocks were separately subjected to phenol extraction. The raftinate of the example was produced in the above manner.

165 pounds stripping steam at the rate of 150 pounds per hour is passed via conduit means 12 to the fourth tray of stripper 10. Vaporous propane at the rate of 40 pounds per hour is passed via conduit means 13 to the lower region of stripper 10. Stripper 1 is operated at a bottom temperature of 500 F., a top temperature of 500 F., and a top pressure of 18 inches of water vacuum. The vacuum is maintained within stripper by a conventional steam ejector 20.

Within stripper 10 the hydrocarbon feed is initially contacted with steam. The stripped hydrocarbon free of solvent and containing moisture passes downwardly from the steam' contact region through stripper 10 into the drying region and is contacted therein with the rising vaporous propane. The propane separates the water from the stripped hydrocarbon.

A vapor stream comprising steam, propane and phenol is drawn from stripper 10 via conduit means 14 and passed to a conventional heat exchange means 16. A partially condensed stream is passed from heat exchange means 16 via conduit means 17 to accumulator 18. A liquid stream comprising phenol and water is withdrawn from accumulator 18 via conduit means 21. The water and phenol stream withdrawn from accumulator 18 via conduit means 21 can be passed, if desired, to a subsequent separation step not herein illustrated for recovery of the phenol from the water. A vapor stream comprising steam and propane is withdrawn from the top of accumulator 18 via conduit means 19.

Rafiinate substantially free of phenol and water is withdrawn from the bottom of stripper 10 via conduit means 22 at the rate of 48,000 pounds per hour. Although as illustrated, the steam stripping and drying steps were conducted in the same stripper vessel, it is within the scope of this invention to employ separate vessels for the steam stripping and vaporous drying steps. The rafiinate withdrawn from stripper 10 via conduit means 22 can be passed to a subsequent propane dewaxing process 23; wherein liquid propane is introduced into said dewaxing process via liquid propane conduit means 24. Under such conditions, the propane absorbed by the rafiinate in the drying region is separated from the raftinate in the pro pane dewaxing process.

It is also within the scope of this invention to separate absorbed drying agent from the rafiinate withdrawn from stripper 10 via conduit means 22 by a subsequent conventional separation process step not herein illustrated.

As will be evident to those skilled in the art, various modifications of this invention can be made, or followed, in the light of the foregoing disclosure, without departing from the spirit or scope thereof.

I claim:

1. A process which comprises contacting a mixture com-prising a hydrocarbon and a component selected from phenol and furfural with steam in a stripping zone, and contacting the resultant steam-stripped hydrocarbon with a vaporous drying agent selected from butane, propane, methylethyl ketone, mixtures of ketones, and a mixture of methylethyl ketone and toluene.

2. A process which comprises introducing a feed mixture comprising a hydrocarbon and a component selected from phenol and furfural into the upper region of a stripping zone, introducing steam into an intermediate region of said stripping zone, introducing a vaporous drying agent selected from butane, propane, methylethyl ketone, mixtures of ketones, and a mixture of methylethyl ketone and toluene into the lower region of said stripping zone, Withdrawing a vaporous fraction comprising steam, said component, and said drying agent from the top of said stripping zone, and withdrawing a substantially water-free hydrocarbon fraction from the bottom of said stripping zone.

3. A process which comprises contacting a rafiinate containing a selective solvent having a greater volatility than said ralfinate with steam in a stripping zone, contacting with a vaporous dewaxing agent the resultant solvent-free raffinate in said stripping zone whereby said rafiinate is rendered substantially water-free, passing the resultant substantially water-free and solvent-free raliinate from said stripping zone to a dewaxing zone, adding to said dewaxing zone as a liquid an additional amount of dewaxing agent precipitating wax crystals in said dewaxing zone by the vaporization of said dewaxing agent, and withdrawing from said dewaxing zone a substantially wax-free lubricating oil fraction.

4. The process of claim 3 wherein each said dewaxing agent is selected from the group consisting of butane, propane, methyl ethyl ketone, a mixture of ketones, and a mixture of methyl ethyl ketone and toluene.

5. The process of claim 4 wherein said selective solvent is selected from the group consisting of phenol and furfural.

6. A process which comprises contacting a rafiinate containing phenol with steam in the solvent-stripping region of a stripping zone, contacting with vaporous propane the resultant phenol-free raffinate in the drying region of said stripping zone, maintaining a temperature and pressure in said drying region in the range of 350- 700 F. and 10 p.s.i.a. to 20 p.s.i.a., respectively, maintaining the weight ratio of vaporous propane to rafiinate in said drying region in the range of 1:500 to 112000, passing the resultant moisture-free and phenol-free rallinate from said stripping zone to a dewaxing zone, precipitating wax crystals in said dewaxing zone by the vaporization of propane introduced into said dewaxing zone as a liquid, and withdrawing from said dewaxing Zone a substantially wax-free lubricating oil fraction.

7. The process of claim 6 to include maintaining a temperature and pressure in said solvent stripping region of said stripping zone in the range of 350-700" F. and 10 p.s.ia. to 20 p.s.i.a., respectively, and maintaining the weight ratio of said steam to said raffinate in the range of 1:150 to 1:500.

8. A process which comprises introducing a feed mixture comprising a hydrocarbon and phenol into the upper region of a stripping zone, introducing steam into an intermediate region of said stripping zone, introducing propane into the lower region of said stripping zone, withdrawing a vaporous traction comprising steam, said phenol, and said propane from the top of said stripping zone, and withdrawing a substantially water-free hydrocarbon fraction from the bottom of said stripping zone.

References Cited UNITED STATES PATENTS 2,192,253 3/1940 Adams 20832l 2,673,174 3/1954 King 208- 321 2,687,982 8/1954 Baumann 208321 2,692,222 10/1954 Packie 208321 DELBERT E. GANTZ, Primary Examiner.

HERBERT LEVINE, Examiner.

S. P. JONES, Assistant Examiner.

Claims (1)

1. A PROCESS WHICH COMPRISES CONTACTING A MIXTURE COMPRISING A HYDROCARBON AND A COMPONENT SELECTED FROM PHENOL AND FURFURAL WITH STEAM IN A STRIPPING ZONE, AND CONTACTING THE RESULATANT STEAM-STRIPPED HYDROCARBON WITH A VAPOROUS DRYING AGENT SELECTED FROM BUTANE, PROPANE,

Images