PROCESS FOR THE PRODUCTION OF PETROLEUM TAR PITCH FOR USE AS A BINDER IN THE PRODUCTION OF ELECTRODES

Abstract

A process for the production of petroleum tar pitch with the using a fresh hydrocarbon feedstock, preheating it, treating the heated feedstock and passing fractionating the treated feedstock into gases, light distillates and a bottom fractionation stream, then dividing the bottom fraction stream into a recycle stream and a cracked fraction stream and using the cracked fraction stream in a reduced pressure distillation tower so that the light cracked fraction is fractionated light vacuum gas oil, heavy vacuum gas oil and a high quality petroleum tar pitch.

Description

BACKGROUND OF THE INVENTION

High quality petroleum tar pitch can be used in a variety of applications. One of the most important uses for high quality petroleum tar pitch is in the manufacture of anodes made from calcined petroleum coke and a binder pitch. The anodes are used in the production of primary aluminum. Presently anodes for use by the aluminum and steel industries are manufactured employing almost exclusively coal tar pitch as the binder. There have been many attempts in the past to produce petroleum tar pitch suitable for use as a binder in the manufacture of electrodes.

In the metallurgical industry, the electrodes are made from petroleum coke and pitch binder. Pitch typically requires the presence of quinoline, and a high residual carbon content. The addition of carbon black into pitch tar is typically done to increase residual carbon and Quinoline insoluble content.

None of the foregoing processes have been able to produce commercial petroleum tar pitch suitable for use as a binder in the manufacture of electrodes for the aluminum and steel industries. It is highly desirable to provide a process for the production of high quality petroleum tar pitch which would allow for the economic production of pitch suitable for the manufacture of electrodes.

Further objects and advantages of the present invention will appear hereinbelow.

SUMMARY OF THE INVENTION

The invention is drawn to a process for the production of petroleum tar pitch by first obtaining a fresh hydrocarbon feedstock and then feeding that feedstock to a pre-heater and thereafter feeding a soaker reactor for treatment under controlled conditions so as to promote condensation and polymerization reactions. The treated feedstock is thereafter passed to a fractionating tower wherein the feedstock is fractionated into gases, light distillates and bottom fraction, then dividing the bottom fraction stream into a recycle stream and a cracked fraction stream, then feeding the cracked fraction stream to a reduced pressure distillation tower wherein the cracked fraction stream is further fractionated into (1) light vacuum gas oil, (2) heavy vacuum gas oil and (3) a high quality petroleum tar pitch, of a quality suitable for use as a binder in the manufacture of electrodes, the petroleum tar pitch is then mixed with a refining element such as anode grade coke to improve the desired petroleum tar pitch product and finally recycling the recycle stream and admixing the recycle stream with the fresh feedstock

The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a schematic flow diagram illustrating the process of the present invention.

DETAILED DESCRIPTION

The present invention is drawn to a process for the production of high quality petroleum tar pitch for use as a binder in the manufacture of electrodes for the aluminum and steel industries. The characteristics of a high quality petroleum tar pitch are the following:

• [Conradson Carbon, (wt. %) 40-60
• Density@15° C., (gr/cc) 1.20-1.25
• Mettler Softening Point, (° C.) 100-125
• Quinoline Insoluble, (wt. %) 0-10]

With reference to the FIGURE, as shown a fresh feedstock is delivered via line 20 for treatment in the process of the present invention. The fresh feedstock is preferably a highly aromatic hydrocarbon stream. Feedstocks suitable and preferred for the process of the present invention are characterized by the following composition and properties:

• [Density@15° C., (gr/cc) 0.8-1.15
• Solids Content, (wt. %) 0-0.1
• Aromatics, (wt. %) 54-85].

Suitable hydrocarbon feeds include highly aromatic hydrocarbon selected from the group consisting of catalytic cracking decanted oil, lubricant extract, Heavy Coker Gasoil (HCGO), Heavy Vacuum Gasoil (HVGO) and mixtures thereof.

The fresh feedstock as defined above can, if desired, be delivered to a filtering station 1 wherein the hydrocarbon stream is filtered so as to remove excess undesirable solids so as to produce a filtered clean stream. In accordance with the present invention it is desired that the product treated in the process of the present invention have a solids content of between 0 to 0.01 wt. %. By filtering the fresh feed, the desired solid content can be obtained. Typical filtration techniques such as centrifugal, electrostatic or mechanical techniques can be used in the filtering station 1. These techniques are sufficient to remove at least 99% of the undesirable solids in the fresh feed stream. The filtered stream preferably has the following properties:

• [Conradson Carbon, (wt. %) 0-7
• Density@15° C., (gr/cc) 0.8-1.1
• Solids Content (wt %) 0-0.01
• Aromatics, (wt. %) 54-85]

The clean filtered stream is thereafter fed via line 21 to a heater 2 wherein the stream is pre-heated. It is desirable in the process of the present invention to mix the filtered stream with a recycle stream in a manner to be described hereinbelow.

The stream fed to the heater or furnace 2 is pre-heated to a temperature of between 380° and 480° C. and thereafter is delivered via line 23 to a soaker type reactor 3. The heated feedstock is treated in the soaker reactor 3 at a temperature of from about 360° to 460° C., a pressure of from about 1480 to 1825 kpa and a residence time of from about 0.25 to 5 hours. This treatment allows condensation and polymerization reactions to take place in the soaker reactor. It is preferred that the treatment in both the heater furnace and soaker reactor take place in an oxygen-free environment and, preferably an inert environment.

The treated stream from the soaker 3 is delivered via line 24 to a fractionating tower 4 where the feedstock is fractionated into gases, which are taken off via line 25, light distillates which are taken off via line 26 and a bottom fraction stream which is taken off via line 27. The fractionator is operated under the following operating conditions: a bottom fractionator temperature of from about 330° to 430° C. and a pressure of from about 101 to 850 kPa.

The yields from the fractionating tower 4 comprises 2 to 8 wt. % C4 -gases and 3 to 8 wt. % light distillates having an ASTM D-86 cut point of between 92° C. and 220° C. based on fresh feed. It is preferred that the treatment in the fractionating tower 4 take place in an oxygen free environment and, preferably, an inert environment.

The bottom fraction drawn off through line 27 is a cracked fraction bottom stream having the following composition and properties:

• [Conradson Carbon, (wt. %) 10-18
• Density@15° C., (gr/cc) 1.1-1.15
• Solids Content, (wt. %) 0-0.01
• Aromatics, (wt. %) 70-95
• Softening Point, (° C.) <25]

In the preferred embodiment of the present invention, a portion of the cracked fraction bottom stream is recycled back to heater 2 or soaker reactor 3 and the remainder is further fractionated in the manner discussed hereinafter.

The portion of cracked fraction forming the recycle stream is preferably recycled via line 28 where it is admixed with the fresh feed prior to delivery of the feed to the furnace 2. In accordance with the present invention, the recycle delivered via line 28 is mixed with the fresh feed in a ratio of up to 3:1 by volume of recycle to fresh feed and preferably in a ratio of about between 2:1 to 3:1. Recycling of the heavy cracked fraction via line 28 is highly desirable in order to optimize the resulting pitch properties obtained in the process of the present invention upon further fractionation.

The remainder of the cracked fraction is delivered via line 29 to a further fractionating unit 5 such as a reduced pressure distillation tower wherein the cracked fraction is further fractionated into light vacuum gas oil taken off via line 30, heavy vacuum gas oil taken off via line 31 and petroleum tar pitch taken off line 33. The cracked fraction is fractionated in distillation unit 5 at a bottom fractionator temperature of between 300° to 380° C. and a pressure of between 0.3 to 15 kPa and preferably in an oxygen-free environment. The petroleum tar pitch resulting from the process of the present invention and drawn off via line 33 is a high quality petroleum pitch having the following properties:

• [Conradson Carbon, (wt. %) 40-60
• Density@15° C., (gr/cc) 1.20-1.25
• Mettler Softening Point, (° C.) 100-125
• Quinoline Insoluble, (wt. %) 0-10]

This petroleum tar pitch is of high quality and suitable for use as a binder in the manufacture of electrodes.

The yield of light vacuum gas oil taken off line 30 is between 15 to 25 wt. %, the yield of heavy vacuum gas oil taken off line 31 is from 30 to 50 wt. % and the yield of petroleum tar pitch taken off line 33 is between 10 to 50 wt. % with all yields being based on fresh feed. The light vacuum gas oil has an ASTM D-86 end boiling point of between 300° to 360° C. and the heavy vacuum gas oil has an ASTM D-1160 end boiling point of between 450° to 570° C.

The petroleum tar pitch taken off via line 33 can, if desired, be delivered to a mixer 6 where it is mixed with an additive selected from the group consisting of fine divided anode grade coke, carbon black, or mixtures thereof via line 36. In accordance with the present invention it is desirable to use the light vacuum gas oil taken off line 30 and heavy vacuum gas oil taken off line 31 as the additive to the mixture 6. It is preferred that the light vacuum gas oil or the heavy vacuum gas oil be mixed with the pitch in an amount of between 3 to 15 volume percent. The preferred light vacuum gas oil has the following composition and properties:

• [ASTM D-86 Initial Boiling Point, ° C. 170-220
• ASTM D-86 Final Boiling Point, ° C. 300-360
• API Gravity 18-28
• Aromatics, wt. % 45-80]
  The preferred heavy vacuum gas oil has the following composition and properties:
• [ASTM D-1160 Initial Boiling Point, ° C. 240-390
• ASTM D-1160 Final Boiling Point, ° C. 450-580
• API Gravity 1-4
• Aromatics, wt. % 45-80]

The heavy vacuum gas oil can also be recycled into the filtered feedstock in a ratio of at least about 0.25:1 by volume recycle stream to fresh feedstock, but preferably a ratio of about between 0.5:1 to 0.8:1 by volume recycle stream to fresh feedstock.

A finely divided anode grade coke, carbon black, or mixtures thereof is admixed with the petroleum pitch in mixer 6. The proportion of the anode grade coke, carbon black, or mixtures thereof mixed with the petroleum pitch should be between 5 to 20 wt. %. Suitable anode grade coke, carbon black, or mixtures thereof for use in the process of the present invention has the following properties:

• [Average Particle Size, microns 12-110
• Apparent Bulk Density, gr/cc 0.46-0.65
• Water Content, wt. % 0-0.2
• Oil Absorption, cc/100 gr 60-75]

The refining additives delivered via line 36 to mixer 6 have the effect to increase Quinoline insoluble content, conradson carbon and softening point. An additive of light vacuum gas oil or heavy vacuum gas oil improves the wettability of the pitch which would reduce the temperature and mixing time necessary when mixed with calcining petroleum coke during the manufacture of electrodes. The modified petroleum pitch product can be delivered via line 34 to a finishing station 7 where it is shaped as pencils or flakes prior to being sent to storage via line 35.

The use of anode grade coke as additive refined with the heavy vacuum gasoil showed improvements in the anodes properties. The use of anode grade coke of the present invention is preferred for multiple reasons. The availability of the product, the low nickel and vanadium content, and the fact that it does not add other foreign agents to the anode. The product performed well during mixing and therefore resulted in excellent quality aluminum. It is for these reasons that anode grade coke was chosen as the preferred refining element

Further, in order to decrease the deposition of solids, a reduction of residence time was implemented and an additional recycling of a cleaner stream with less contaminant content was introduced through line 32.

The process of production of tar pitch is a moderate thermal cracking process, which uses polymerization reactions, cracking and condensation to transform the load in a binder. The recycling step is important because it increases the conversion rate and the production of binder pitch.

It is to be understood that the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are susceptible of modification of form, size, arrangement of parts and details of operation. The invention rather is intended to encompass all such modifications, which are within its spirit and scope as defined by the claims.

Claims

1. A process for the production of petroleum tar pitch comprising:

a. providing a fresh hydrocarbon feedstock;

b. pre-heating at least a portion of the feedstock in a furnace to a temperature of about 380° to 480° C.;

c. feeding at least a portion of the heated feedstock to a reactor and treating at least a portion of the heated feedstock in the reactor under controlled conditions so as to promote condensation and polymerization reactions;

d. passing at least a portion of the treated feedstock to a fractionating tower wherein at least a portion of the treated feedstock is fractionated into (1) gases, (2) light distillates and (3) a bottom fractionation stream;

e. dividing the bottom fraction stream into a recycle stream and a cracked fraction stream;

f. feeding the cracked fraction stream to a reduced pressure distillation tower wherein the light cracked fraction is further fractionated into (1) light vacuum gas oil, (2) heavy vacuum gas oil and (3) a high quality petroleum tar pitch;

g. recycling the recycled stream and admixing the recycle stream with the fresh feedstock; and

h. mixing the petroleum tar pitch with a refining element in the form of anode grade coke, to create a petroleum tar pitch product.

2. A process according to claim 1 wherein the feedstock is a highly aromatic hydrocarbon selected from the group consisting of catalytic cracking decanted oil, lubricant extract, Heavy Coker Gasoil (HCGO), Heavy Vacuum Gasoil (HVGO) and mixtures thereof and has the following composition and properties:

[Density@15° C., (gr/cc) 0.8-1.15

Solids Content, (wt. %) 0-0.1

Aromatics, (wt. %) 54-85].

3. A process according to claim 1 wherein the light vacuum gas oil has the following properties:

[ASTM D-86 Initial Boiling Point, ° C. 170-220

ASTM D-86 Final Boiling Point, ° C. 300-360

API Gravity 18-28

Aromatics, wt. % 45-80].

4. A process according to claim 1 wherein the heavy vacuum gas oil has the following properties:

[ASTM D-1160 Initial Boiling Point, ° C. 250-320

ASTM D-1160 Final Boiling Point, ° C. 450-520

API Gravity 0-9

Aromatics, wt. % 45-95].

5. A process according to claim 1 wherein the petroleum tar pitch has the following properties:

[Conradson Carbon, (wt. %) 40-60

Density@15° C., (gr/cc) 1.20-1.25

Mettler Softening Point, (° C.) 100-125

Quinoline Insoluble, (wt. %) 0-10].

6. A process according to claim 1 wherein the refining element added is anode grade coke and it is added in an amount of between 5 to 20 wt. % of the petroleum pitch.

7. A process according to claim 1 wherein the finely divided anode grade coke has the following properties:

[Average Particle Size, microns 12-110

Apparent Bulk Density, gr/cc 0.46-0.65

Water Content, wt. % 0-0.2

Oil Absorption, cc/100 gr 60-75].

8. A process according to claim 1 wherein the petroleum tar pitch product is delivered to a finishing station to be shaped.

9. A process according to claim 1 wherein at least a portion of the feedstock is filtered to produce a feedstock having a solid content of 100 ppmw.

10. A process according to claim 9 wherein the filtering is done by centrifugal, electrostatic or mechanical techniques.

11. A process according to claim 9 wherein the filtering removes at least 99% of solids.

12. A process according to claim 9 wherein the filtered feedstock has the following composition and properties:

[Conradson Carbon, (wt. %) 0-7

Density@15° C., (gr/cc) 0.8-1.1

Solids Content (wt %) 0-0.01

Aromatics, (wt. %) 54-85].

13. A process according to claim 9 wherein the filtered feedstock is heated to a temperature of between 380 and 480° C. to provide a heated feedstock.

14. A process according to claim 13 wherein the heated feedstock is passed to a soaker reactor, plug flow reactor or batch reactor, and wherein the feedstock is treated in the reactor at condensation and polymerization conditions to provide a treated feedstock.

15. A process according to claim 14 wherein the conditions include a temperature between 360 and 460° C., a pressure between 1480 and 1825 kpA, the conditions are oxygen free and inert and are held between 0.25 and 5 hours.

16. A process according to claim 14 wherein the treated feedstock is passed to a fractionating tower wherein the treated feedstock is fractionated into (1) gases, (2) light distillates and (3) a bottom stream.

17. A process according to claim 1 wherein step (d) takes place under the following conditions:

[Temperature, ° C. 330-430

Pressure, kPa 101-850

in an inert environment and substantially oxygen free].

18. A process according to claim 16 wherein the treated feedstock is fractionated to yield:

2 to 8 wt. % C4-gases

3 to 8 wt. % light distillates having an ASTM D-86 cut point of between 92° C. and 220° C. based on fresh feed and a bottom stream.

19. A process according to claim 16 wherein the bottom stream is divided into a recycle stream and a cracked fraction bottom stream.

20. A process according to claim 19 wherein the cracked fraction bottom stream has the following composition and properties:

[Conradson Carbon, (wt. %) 10-18

Density@15° C., (gr/cc) 1.1-1.15

Solids Content, (wt. %) 0-0.01

Aromatics, (wt. %) 70-95

Softening Point, (° C.) <25].

21. A process according to claim 19 wherein the recycle stream is admixed with the filtered feedstock in a preferred ratio of between 2:1 and 3:1 by volume of recycle stream to fresh feedstock.

22. A process according to claim 19 wherein the recycle stream is mixed with the filtered feedstock.

23. A process according to claim 19 wherein the recycle stream is mixed with the filtered feedstock in a ratio of up to 3:1 by volume recycle stream to fresh feedstock.

24. A process according to claim 19 wherein the cracked bottom stream is further fractionated to yield Light Vacuum Gas Oil, Heavy Vacuum Gas Oil and a high quality petroleum tar pitch.

25. A process according to claim 24 wherein the cracked bottom stream is further fractionated under the following conditions: bottom fractionator temperature 300-380° C., 0.3-15 kPa pressure, in an inert and a substantially oxygen free environment.

26. A process according to claim 24 wherein the cracked bottom stream is further fractionated to yield the following products:

[ASTM D-1160 End Point Wt. %

Light Vacuum Gas Oil 300-360° C. 15-25

Heavy Vacuum Gas Oil 450-570° C. 30-50

Petroleum Tar Pitch 15-50].

27. A process according to claim 24 wherein the Heavy Vacuum Gas Oil is recycled into the filtered feedstock in a ratio from about 0.25:1 by volume recycle stream to fresh feedstock.

28. A process according to claim 24 wherein the heavy vacuum gas oil is recycled into the filtered feedstock in a ratio of about between 0.5:1 to 0.8:1 by volume recycle stream to fresh feedstock.

29. A process according to claim 1 wherein the refining element further comprises fine divided carbon black.

30. A process according to claim 1 wherein the refining element further comprises anode grade coke and low metals and sulfur content coke.