CA1203190A - Pitch demetalization by destruction distillation - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Pitch (the faction boiling above 524°C) of low metals content is produced by delayed coking of a heavy hydrocarbon oil with a high metals content. In a first delayed coking step, the gaseous and liquid phase is removed and sent to a fractionation unit. The bottoms from the fractionation unit are (a) subjected to a second delayed coking to produce coke which meets electrode grade specifications for metals, or (b) catalytically hydrocracked for conversion of distillate products. The demetalized pitch produced in the first delayed coking operation is also a valuable product for use as a binder in the production of coke for electro-metallurigical applications.

Description

This invention relates to the demetalization of heavy hydrocarbons, and in particular to a process for producing demetalized pitch.
In yeneral, heavy hydrocarbon oils contain a fraction boiling above 52AC. 5uch fraction is called "pitch". Delayed coking, which is also known as destructive distillation, is used to upgrade the pitch to produce valuable product~ and coke.
The coke produced from this process may be used to manufacture electrodes for electro-metallurigical applications (e.g., in the aluminium refining industry). The starting materials for the production of such cokes are necessarily low in contaminants, particularly sulphur and heavy metals, e.g. nickel and vanadium.
The starting materials are typically naphthenic crudes, decant oils from fluid catalytic cracking units, tars from the thermal cracking of delayed coker gas oil, pyrolysis tars, filtered or centrifuged coal tars and pitches or blends of such materials with varying amounts of residual oils. However, when the starting material to a delayed coker contains high concentrations of metals such as vanadium and nickel, the coke produced is cont~m;n~ted by the metals and has little market value.
Delayed coking is a well known operation familiar to all with a knowledge of the art of petroleum refining. It is generally the first step in the processing of tar sands bitumen, heavy and residual oils producing valued liquid and gaseous products and a solid phase or coke. The operating conditions and process steps are well known, and one of the earliest descriptions of these is that in an article by J. Diwoky in Refiner and ~atural Gasoline Manufacturer, Vol. 17, No. 11, Nov. 1938. The present invention utilizes this type of coking operation, but in a novel tandem mode utilizing a process ~3:~L9C~

derived feedstock, U.S. Patent No. 3,617,~80, issued to H.~. Keel on November 2, 1971 described delayed coking in a second stage blocked out operation of a process stream derived from delayed coking of a topped, reduced or vacuum reduced asphaltenic or naphthenic crude oil. The process yields a superior quality petroleum coke. ~lowever, the patent does not address demetali-zation of the feed during the first stage delayed coking operation.
V.S. Patent No. 3,769,200, issued to H.O. Folkins on October 30, 1973 teaches that limited coking during the first stage of a two stage delayed coking operation produces an in-organic contaminant, particularly metals, free coke. Metals contaminants are removed from the feed via filtration on a bed of coke formed during the first stage coking operation. However, the first stage delayed coking operation does not fully coke the feed and requires that the first stage coking operation be carried out in a batch mode, with the preferred em~odiment in the unusual down flow mode, such that the filtered effluent may be withdrawn and sent to the second delayed coking operation.
The process does not withdraw the demetalized effluent continu-ously from the vapour phase produced in the first stage delayed coking operation as a fraction contalning a significant ~uantity of material boiling over 524C.
U.S. Patent No. 3,959,115, issùed to K. Hayashi et -al on May 25, 1976 teaches that the production of high grade needle type petroleum coke can be achieved by heat soaking of oil in a tube heater at 460C-520C at 5-20 kg/m2 g for 30-500 seconds, and then subjecting the oil to delayed coking under relatively mild conditions. The uncoked heavy residual is -" ~Z03~g~

subsequently subjected to a second delayed cokin~ operation under relatively severe conditions.
Other two stage fluid coking processes are disclosed in U.S. Patents Nos. 2,854,397, issued to J.F. ~oser on September 30, 1958; 2,879,221, issued to J.W. Brown on March 29, 1959 and 3,671,424 issued to A.L. Saxton on June 20, 1972. Canadian Patent No. 1,143,315 issued to W.J. Metrailer on March 22, 19~3 teaches that fluid coking followed by delayed coking produces a coke with a low metals content.
The object of the present invention is to provide a relatively simple process for producing demetalized pitch.
Accordingly, the present invention relates to a process for producing demetalized pitch from a heavy hydro-carbon oil comprising -the steps of:
(a) first delayed coking the hydrocarbon oil at a temperature of 400 to 500C and a pressure of 0.1 to 1.0 MPa; and (b) recovering a high boiling fraction from the liquid coking product by fractionation of the liquid coking product wherein a substantial portion boils above 524C.
The process can be used for the treatment of bitumen, heavy oils or residuum from conventional oils, all referred to as heavy hydrocarbon oils. The normal method of recovering the high boiling fraction is by transferring a product stream containing a gaseous and a liquid phase from the coking oper-ation to a fractionation unit. The demetalized pitch produced from the first stage delayed coking operation ~a) is itself a valuable product for use as a binder in the production of coke ~or electro^metallurgicalapplications.

3~96~

The invention will now be described in greater detail with reference to the accompanyiny drawinas, which illustrate apparatuses for carrying out preferred embodiments of the invention, and wherein:
Figure 1 is a schematic flow diagram of a bench scale delayed coker;
Figure 2 is a schematic flow diagram of an apparatus for carrying out a first embodiment of the invention; and Figure 3 is a schematic diagram of an apparatus for carrying out a second embodiment of the invention.
EXPERIMENTAL APPARATUS
Referring to Fig. 1, feed from a tank or hopper 1 is fed through a line 2 by a pump 3 to a preheater 4. The temp-erature of the feed is increased to 350~C in the heater 4 and then increased to reaction temperature using an isothermal sand bath. In the early stages of the operation, feed from the sand bath heater is directed through a line 5, a three-way valve 6 and a line 7 to a slop tank 8 for one hour so that operating conditions, i.e. pressure, feed rate and temperature can stabilize. Once conditions have stabilized, feed is switched dir~ctly through a line 9 and from the valve 6 to a coking drum 10 .
In the drum 10, the feed is thermally cracked to product coke and hydrocarbon products. The liquid and gaseous products are discharged via line 11 to a water cooled condenser 12, and are then separated in a separator 13. Gas samples from the separator 13 pass through a line 14 and valve 15 to a gas sampling station 16. Gas samples are analyzed by gas chromato-graphy. The gas volume is monitored using a wet test meter 17, and is scrubbed in a scrubber 18 prior to venting via line "~ ~L2~3~9C~

19. All liquid products from the sep~rator 13 pass through a three-way valve 20 to a receiver 22 for the first two hours, and then to receiver 23 for the next two hours. Coke drum pressure is monitored and controlled by a back pressure controller (not shown).
The chemical and physical quality of the coke is largely determined by the characteristics of the feedstock.
However, the coking process itself influences final properties of the coke, particularly the volatile content, density and hardness. Various techniques have been used to screen coker feedstocks. The bench-scale technique usually involves batch operation in an autoclave where static coking takes place.
However, the bench-scale unit used in this study consisted of a small scale delayed coker designed as a scaled down version of commercial units. Operating conditions were varied over a wide range to attain product distribution similar to com-mercially reported yields. Operating procedures used in the laboratory differed from large scale delayed cokers and a brief comparison of bench~scalewith commercial operating procedures is given below:
LABORATOR~ COKER CO~ERCIAL COKER
Coke drum is heated Coke drum is insulated, drum externally to compensate temperature maintained by for heat losses. fresh feed.
Only fresh feed is used Optional recycle of heavy in a once-through option. fuel oil material from fractionator to extinction.
No stripping of coke. Steam stripping.
The comparison shows that the laboratory scale coker evaluates feedstocks effectively since operating conditions are `` ~203~90 easily controlled, i,e. coking temperature, recyclin~ and coke handling. Experimental results show that the coke produced in the bench-scale coker is similar to that produced commercially.
The pitch (material boiling above 524C) entrained in the liquid products is found to contain only a small fraction of the metals typically found in the feed pitch.
It has been found that demetalizing oE the pitch fraction present in heavy hydrocarbon oils occurs during delayed coking under selected operating conditions. Demetali-zing is observed in the pressure range 0.1 to 1.0 MPa and attemperatures between 410 and 490C. We have found that delayed coking of the recycle stream from a commercial delayed coker yields coke which meets anode grade specifications for metals content. The recycle stream is derived from a feed containing a high concentration of metals, whereas the recycle stream contains pitch with a significantly reduced metals content.

FUL~ SCALE APPARATUSES `
Referring to Fig. 2 of the drawings, a suitable apparatus for carrying out one embodiment o the process of the present invention includes a feed reservoir 30 for a heavy hydrocarbon oil, a substantial portion of which boils above 524.
Oil is pumped from the reservoir 30 through a line 31 to a heater 32using a pump 33. The oil is heated to reaction temp-erature in the heater 32 and fed through line 34 to a delayed coker 35. In the delayed coker, the oil undergoes thermal cracking to produce coke and a product stream, which is discharged via line 36, valve 37 and line 38 to a distillation tower 40.
The liquid and gaseous products (overheads) are dis-charged from the tower 40 through line 41 for refining. The ~203~9(~
.,, ~

bottom stream is discharged from the tower 40 through line 42, and pumped through a heater 43 and line 44 to a second stage delayed coker 45 using a pump 46. The coke produced in the second stage coker 45 is of higher quality than that produced in the first stage and can be marketed as a speciality carbon.
The effluent from the coker 45 is passed through line 47 to the valve 37 for mixing with the first stage product stream and returned to the distillation tower 40. The bottoms stream of the tower 40 is recycled to extinction in the second stage delayed coker 45. The bottoms stream from the tower 40 can be passed through a line 49 to a storage container 50, and later fed to the line 42 and the pump 46 through a line 51. With this arrangement, sufficient bottoms can be stored for a single pass through the coker 35, whereby the need for a separate delayed coker specific for such opera-tion is avoided.
The basic apparatus of Fig. 3 is similar to that of Fig. 2 and accordingly, wherever possible, the same reference numerals have been used to identify the same or similar elements.
In the apparatus of Fig. 3, the product stream from the delayed coker 35 is fed through the lines 36 and 53 to the tower 40.
Liquid and gaseous products from the tower 40 are discharged through the line 41 for refining. The bottoms from the tower 40 are fed through a line 54, pump 55, a heater 56 and a line 57 to a catalytic hydrocracking device 58. Hydrogen gas under high pressure is introduced into the bottoms upstream of the heater through line 59. The products of the device 58 are fed through line 60 to a separator 61. Gases from the separator 61 are fed through a line 62 to a scrubber 63, where the hydrogen gas is scrubbed and passed through line 64 for mixing with make-up hydrogen in line 59. The liquid product from the 3~

separator 61 is passed through line 65 and 53 to the tower ~0.
The bottoms stream from the distillation tower 40 can be re-cycled to extinction with a small drag stream to prevent build-up of metals in the circuit. In this embodiment of the invention, the pitch product is further upgraded by conventional hydrocracking technology. Since the metals content of the pitch is significantly reduced, there is little fouling of catalysts due to metals deposition.
Unlike earlier methods, the process of the present invention yields ademetalized pitch as opposed to a liquid product which is substantially free of metals. This distinction is drawn, because the liquid product from a delayed coker need not contain any pitch depending on the mode of operation. By carrying out the process described hereinbefore, the amount of pitch produced is maximized while a low metals content in the pitch is maintained.

Claims (6)

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

1. A process for producing demetalized pitch from a heavy hydrocarbon oil comprising the steps of:
(a) first delayed coking the hydrocarbon oil at a temperature of 400 to 500°C and a pressure of 0.1 to 1.0 MPa; and (b) recovering a high boiling fraction from the liquid coking product by fractionation of the liquid coking product wherein a substantial portion boils above 524°C.

2. A process according to claim 1, including the step of subjecting said high boiling fraction to a second delayed coking to yield a coke with a low metals content.

3. A process according to claim 1, wherein said high boiling fraction is subjected to catalytic hydrocracking to yield a liquid product while reducing the yield of coke produced.

4. A process according to claim 1, including steam or a light hydrocarbon oil into the hydrocarbon oil during the first delayed coking to promote a greater recovery of pitch in the liquid product.

5. A process according to claim 1 including a plurality of delayed coking steps for providing feed for the fractionation step.

6. A process according to claim 2, wherein the first and second delayed coking steps are effected in a single coker.

q