CA1069846A - Process for making pitch from ethylene bottoms - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Pitch fractions are obtained from highly aromatic feedstock, such as bottoms derived from the production of olefins, by distillation at below about 750°F. under reduced pressure, The product pitch is homogeneously miscible with coal tar or petroleum pitches and is useful as an extender therefor.

Description

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This present invention relates to the manufacture of pitch from highly aromatic feedstock, such as ethylene bottom oils. More specifically this invention relates to recovering pitch fractions from ethylene bottom oils obtained in the production of olefins such as ethylene.
Heretofore, as disclosed in U.S. Patent No.
3,794,579, granted to Enomoto et al., on February 26, 1974, it was known to treat ethylene bottom oils in a multi-step process to obtain pitch fractions. For instance, the first step in this patent involves a heat treatment or "soaking"
of the ethylene bottom oils at temperatures of 400-600C.
for 10-1200 seconds under the extreme pressure of 20-200 kg/cm. The second step requires separation by flashing or i distillation. And the third step involves subsequent heat ~ -treatment at 300-480C. for extended periods of 1-10 hours, again under superatmospheric pressures of up to 50 kg/cm.
It is seen that prior art processes require many steps and severe conditions.
It has now been found that desirable pitch fractions are obtainable from ethylene bottom oils without heat soaking and without extreme pressures, by a simple convenient process which may be batchwise or continuous.
It is an object of this invention to provide a pro-cess for obtaining pitch fractions from ethylene bottoms with-out the concommitant production of large quantities of coke.

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~ J -3-1 It is a further object of this invention to provide a process as aforesaid without extreme pressure conditions and extensive soaking and heating.
It is still a further object of this invention to provide a process as aforesaid yielding pitch fractio~s which are miscible with coal tar pitches and petroleum pitches and thus may be used as extenders therefor.
The a~oresaid, as well as other objects and advan-tages will become apparent from a reading of the following ~, specification and claims.
The oils used as a starting material in this inven-tion are highly aro~atic by-product oils or bottoms from the production of olefins, generally used as feedstock for the production of pitch, such as ethylene, propylene, etc., pre-pared by the thermal cracking of light frac~ions of petroleum oil such as naphtha~ kerosene, light oil, etc., at 700-950C.
Generally the feedstock employed in the present invention are oils having a high content of aromatic compounds comprised substantially of fractions having a boiling point higher than 150C. obtained by various thermal or catalytic crackings of petroleums. These by-product oils, or bottoms, have different properties depending on the conditions of cracking and the con-ditions of distillation after cracking, but such changes of properties have little or no bearing on the practice of the ; .

~ 4-1 process of this invention. Particularly pre~erred by-product oils are those having a high content of aromatic compounds, i.e. over 80% and generally are comprised of more than 80V/o of fractions having boiling points higher than 200C.
Pursuant to this invention the highly aromatic ethylene bottoms are vacuum and/or steam stripped at tempera-tures in the range of about 500 F. to about 750F. at sub-atmospheric pressure. In a batchwise process the stripping may be accomplished in several hours, preferably at tempera-tures below 725 F. Vacuum is maintained~ for instance, atup to 20 inches of Hg, and for ~rom 3 to about 5 hours at about 600-700F. during ba~chwise distillation. Generally a reduced atmosphere of from about 15-20 inches o~ Hg is preferred at a temperature of between 600-700F. Steam stripping and vacuum drawing can be done simultaneously and generally continuously.
The process is adaptable to batchwise as well as continuous processes as seen in the appended examples. In the continuous fractionating process similar conditions as in the batchwise process are applied to a smaller volume in less time. The light ends are distilled off by flashing, vacuum or steam stripping, or combination o~ these, as known in the art. Where it is undesirable to have the light oils ~rom either process contaminated with water, o~ course~ steam .

~Q~9~9L6 1 stripping is omitted and only vacuum is employed.
In using stripping steam, normal quantities and thermal properties of conventional stripping steam are employed, as known in the art. The product fraction distilling below the maximum temperature of about 750F. is collected in vapor traps or condensers, while the desired substantially coke-free residue remains in the process reaction vessel, from which it is recovered. The fraction collecting in vapor traps or condensers may be utilized, for instance, as a fuel oil.
Pitches from ethylene bottoms produced pursuant to this invention generally have the following typical properties:

Melting Point ~Mettler) 100-110 C.

- Specific Gravity (25C./25C.) ~1.25 Benzene Insolubles 15-25V/o By Weight ; Quinoline Insolubles 0-1.0% By Weight Conradson Carbon 40-50% By Weight Distillation:
~ASTM D 20-55) 0-360C. 8-14% By Weight Residue ~Pitch) 85-90% By Weight Quinoline insolubles (ASTM 2318-66) are generally less than 2.0% by weight9 preferably less than about 0.5% by weight. The low quinoline insolubles ~raction is a measure 1 of the coke-free aspect of this product. The di~ference between the benzene insolubles fraction and the quinoline insolubles fraction is indicative of the amount of high molecular weight aromatics.
The present invention is illustrated in greater detail by the following examples.

_ MPLE I

1 A batch distillation vessel is charged wi~h 8673 gallons of ethylene bo~toms having a specific gravity of 1.132 at 60F. and 16.08 percent by weight fixed carbon (FC).
The feedstock is heated to about 660F. and steam stripped.
Vacuum is maintai.ned at below 20 inches of Hg for the last three hours, until a pitch is ob~ained having the desired properties. A pump is used to recirculate the charge at about 40 gallons per minute.
The following Table I reports the conditions and results of this Example.

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~, 1 Steam stripping is started, as indicated in Table I, at 9~ hours after starting, i.e. when the vessel temperature reaches about 660 Fo Samples of the residue taken at various times analyze as reported below in Table II.

TABLE II

Time Pitch (Hours) Dis~illate~

1 0 16.08% FC2 `10 7~ 15 20.66% FC
8 20 23.40% FC
8~ 25 23.83% FC
9~ 30 60 C. M.P~
11 35 70.5C. M.P.
11~ 40 83,3 C. M.P.
12~ 45 96.6C. M.P.
13 50 102.9C. M.P.
15~ 50 103.1 C. M,P, *Quinoline Insolubles 0.36% By Weight Benzene Insolubles16.24% By Weight Conradson Carbon47.35% By Weight 1. Percent by weight of charge off.

2. Fixed carbon, weight percent.

3. Melt point - Mettler determination.

_9_ 1 An analysis was made of the collected distillate as follows:

Specific Gravity 1.016 @ 38 C./15.5 C.
Water Content 1.3% By Weight Distillation:
170C. - 0%
210C. - 0%
235C. - .77%
270C. - 13.55%
315C. - 68.92%
355C. - 88.96%

10~30~o Residue _ PLE II

1 A second run is performed with the apparatus and procedures of Example I employing an ethylene bottoms feed-stock having a 1.160 specific gravity at 60F. and 20. 73~/o by weigh~, of FC.
Table IV reports the amount of distillate and analysis of the pitch fractions at various points in the process.

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1 As shown ln Table IV, the steam stripping is con-ducted for approximately the inal 3 hours of the approximately 9 hour process, starting at a point where the tempera~ure is about 600F.; the temperature does not exceed 700F. during the stripping, for best results.
The collected distillate of Example II is analyzed as follows:

Speciic Gravity 1.021 @ 38C./15.5C.
Water Content 1.2% By Weight Distillation:
170C - 0% 270C. - 9.31%
210C. - 0% 315C. - 57.44%
235C. - 1.89% 355C. - 86.71%

12.10% Residue The maximum vessel temperature for Example II is The physical properties of the pitch produced pur-suant to this invention permit such pitch to be employed with pitch derived from both coal tar and petroleum pitch manufac-tured by other processes, and particularly useful as electrodebinder pitch. Other uses of the pitch o this invention include fiber board pitch, paper pipe saturant, and foundry pi~ch blnder.
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EXAMPLE III

1 The ethylene bo~toms pi~ch product of Example II
is mixed under agita~ion with a commercial coal tar pitch in 20% by weight of ethylene bot~oms pitch to 80% by weight of commercial grade coal tar pitch and found ~o be ~horoughly compatible. It enhances the coal tar pitch by compatible dilution to make it more suitable as a pitch product for a particular application. The mixture analyzes ~s follows:

Melting Point O
(Mettler) 110.8 C.
Specific Gravity 1.311 @ 25C./25C.
Fixed Carbon 44.12%

Coke Residue-Modified Conradson 57.61%
Ash 0.12%
Sulfur 0.533%
Benzene Insolubles 31.57%

Carbon Disulfide Insolubles 20.02%
Quinoline Insolubles 12.60%

Distillation:

4,16% off at 0 - 360C.
Residue:
95.05%

- 1 $ -EXAMPLE IV

1 The ethylene bot~oms feedstock as in Example I is passed through a tube still heater in~o a distillation steam stripping column of approximately 12 bubble cap trays midway at 725F. The light fraction is distilled overhead and is contacted with reflux. The temperature at the top of the tower is about 575F. The higher boiling materials which contain the desired bottoms flow downward through the column and contact with stripping steam at a rate of .1-2 lbs. per gallon. Undesired light oils are dis~illed through the over-head section of the column. The final pitch is collected from the bottom of the column at 680F. The properties of the resultant pitch is similar to that of Example I.

~ 6 -16-EXAMPLE V

1 The ethylene bottoms feedstock as in Example II is passed through a tube still heater into a vacuum distillation column of approximately 20 trays midway at 725 F., under about 20 inches Hg. The light fraction distillate overhead is con-tacted with reflux. The temperature at the top o~ the tower is about 600F. The higher boiling material, which contains the desired final pitch, flows downward through the column and is discharged at 680F. The properties of the resulting pitch is similar to that from the batchwise operation in Example II.

From the foregoing data and disclosure, it will be apparent that the present invention makes possible the ready formation of a substantially coke-free ethylene bottoms pitch by convenient no~el process.

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Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for making a pitch product from a highly aromatic feedstock comprising removing light ends under reduced pressure from said feedstock, at a temperature in the range of 600-725°F at 15-20 inches of Hg vacuum and recovering the desired residual pitch therefrom; said pitch having a Mettler M.P. of 100-110°C., Specific Gravity of about 1.25 at 25°C/25°C, Benzene Insolubles of 15-25% Quinoline Insolubles of less than 1.0% and a Conradson Carbon of 40-50% by weight.

2. The process of claim 1, wherein said pitch product has a quinoline insolubles of less than about 0.5 percent by weight as determined by ASTM 2318-66.

3. A process as in claim 1 wherein the feedstock is derived from ethylene bottoms.