Mineral oils: processes and products – Refining – Sulfur removal
Reexamination Certificate
1999-09-17
2001-05-15
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Refining
Sulfur removal
C208S20800M, C208S209000, C208S210000, C208S211000, C208S217000
Reexamination Certificate
active
06231752
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a process for the removal of mercaptans from petroleum distillate streams. More particularly the invention relates to a process wherein the petroleum distillate contains diolefins which are selectively reacted with the mercaptans to form sulfides. Most particularly the invention relates to a process wherein the reaction of the mercaptans with the diolefins is carried out simultaneously with a fractional distillation to remove the sulfides, and thus the sulfur, from the distillate.
2. Related Information
Petroleum distillate streams contain a variety of organic chemical components. Generally the streams are defined by their boiling ranges which determine the compositions. The processing of the streams also affects the composition. For instance, products from either catalytic cracking or thermal cracking processes contain high concentrations of olefinic materials as well as saturated (alkanes) materials and polyunsaturated materials (diolefins). Additionally, these components may be any of the various isomers of the compounds.
The petroleum distillates often contain unwanted contaminants such as sulfur and nitrogen compounds. These contaminants often are catalyst poisons or produce undesirable products upon further processing. In particular, the sulfur compounds can be troublesome. The sulfur compounds are known catalyst poisons for naphtha reforming catalysts and hydrogenation catalysts. The sulfur compounds present in a stream are dependent upon the boiling range of the distillate. Mercaptans are most commonly found in the lower boiling range distillates such as the “front end” of a full boiling range naphtha.
The most common method of removal of the sulfur compounds is by hydrodesulfurization (HDS) in which the petroleum distillate is passed over a solid particulate catalyst comprising a hydrogenation metal supported on an alumina base. Additionally copious quantities of hydrogen are included in the feed. The following equations illustrate the reactions in a typical HDS unit:
RSH+H
2
→RH+H
2
S (1)
RCl+H
2
→RH+HCl (2)
2RN+4H
2
→RH+NH
3
(3)
ROOH+2H
2
→RH+H
2
O (4)
Typical operating conditions for the HDS reactions are:
Temperature, ° F.
600-780
Pressure, psig
600-3000
H
2
recycle rate, SCF/bbl
1500-3000
Fresh H
2
makeup, SCF/bbl
700-1000
As may be seen the emphasis has been upon hydrogenating the sulfur and other contaminating compounds. The sulfur is then removed in the form of gaseous H
2
S, which in itself is a pollutant and requires further treatment.
The naphtha stream from either a crude distillation column or fluid catalytic cracking unit is generally fractionated several times to obtain useful cuts. The full boiling range naphtha (C
4
-430° F.) may first be debutanized to remove C
4
and lighter materials as overheads in a debutanizer, then depentanized to remove C
5
and lighter materials as overheads in a depantanizer (sometimes referred to as a stabilizer) and finally split into a light naphtha (110-250° F.) and a heavy naphtha (250-430°).
U.S. Pat. No. 5,510,568 (Hearn) discloses a process for removing mercaptans from a distillate feed in a distillation column reactor by reacting the diolefins in the feed to form sulfides in the presence of a Group VIII metal catalyst and hydrogen. U.S. Pat. No. 5,321,163 (Hickey et al) discloses a similar process with an etherification zone also positioned in the distillation column reactor. In both of these processes the distillate feed is fed below the catalyst bed.
One advantage of the present invention is that the present process allows the use of existing debutanizers which are higher pressure than existing gasoline splitters thus providing the appropriate temperatures in the thioetherification bed not obtainable in the low pressure gasoline splitters. The complete gasoline stream through the end point is contacted with the thioetherification catalyst, thus the mercaptans throughout the gasoline range are reacted to heavier thioetherification. Other advantages and features of the present invention will become apparent from the following description.
SUMMARY OF THE INVENTION
The present invention presents an improved process for the removal of mercaptans from a full boiling range (C
4
-430° F.) cracked naphtha stream. The cracked naphtha contains C
4
's to C
8
's components which may be saturated (alkanes), unsaturated (olefins) and poly-unsaturated (diolefins) along with minor amounts of the mercaptans. The full boiling range naphtha is debutanized in a fractional distillation column to remove that portion containing the C
4
and lower boiling materials (C
4
−) as overheads and the C
5
and higher boiling materials (C
5
+) as bottoms. The present invention utilizes the lower portion of the debutanizer to react substantially all of the mercaptans contained in the full boiling range cracked naphtha with a portion of the diolefins to form sulfides (thioethers). Any methyl mercaptan present would be in the C
4
fraction and may be reacted and removed in a small catalyst bed positioned above the naphtha feed. The sulfides (including any made in an upper bed) are removed as bottoms from the debutanizer column along with the C
5
+ which is passed on to a depentanizer type distillation column where the sulfides are removed with the bottoms C
6
+ (or C
7
+) and a C
5
or (C
5
/C
6
) fraction having reduced sulfur is recovered overhead. The sulfides in the bottoms may be hydrogenated in a separate distillation column reactor or a non distillation fixed bed to cleave the sulfide thereby producing H
2
S and hydrogenating diolefins. The H
2
S separated therefrom is non-condensibles.
The catalyst used for the sulfide reaction is a supported Group VIII metal such as nickel sulfide, e.g., nickel/molybdenum on an alumina base which is conveniently configured as a catalytic distillation structure.
In the sulfide reaction, hydrogen is provided as necessary to support the reaction and to reduce the oxide and maintain it in the hydride state.
The present process preferably operates at overhead pressure of sulfide (first) distillation column reactor in the range between 50 and 200 psig and temperatures within said distillation reaction zone in the range of 100 to 400° F., preferably 130 to 270° F. The hydrogen partial pressure is between 0.01 and 30 psi. The conditions for this separation are fortuitously appropriate for the sulfide reaction. The pressure selected is that which maintains catalyst bed temperature between 100° F. and 400° F.
The term “reactive distillation” is sometimes also used to describe the concurrent reaction and fractionation in a column. For the purposes of the present invention, the term “catalytic distillation” includes reactive distillation and any other process of concurrent reaction and fractional distillation in a column regardless of the designation applied thereto.
REFERENCES:
patent: 5321163 (1994-06-01), Hickey et al.
patent: 5510568 (1996-04-01), Hearn
patent: 5595634 (1997-01-01), Hearn et al.
patent: 5597476 (1997-01-01), Hearn et al.
patent: 5807477 (1998-09-01), Hearn et al.
patent: 5863419 (1999-01-01), Huff, Jr. et al.
patent: 6090270 (2000-07-01), Gildert
patent: WO 96/18704 (1996-06-01), None
Catalytic Distillation Technologies
Griffin Walter D.
Johnson Kenneth H.
LandOfFree
Process for the removal of mercaptans does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for the removal of mercaptans, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the removal of mercaptans will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2475708