US3298947A - Producing purified fluid coke - Google Patents

Description

United States Patent PRODUCING PURIFIED FLUID COKE C F Gray, Baton Rouge, La., assignor to Esso Research and Engineering Company, a corporation of Delaware N0 Drawing. Filed May 6, 1963, Ser. No. 278,446 6 Claims. (Cl. 20846) This invention relates to treating coke especially fluid coke particles made by the fluid coking process to render the coke suitable for use such as in electrodes or other products 'where impurities'should be at a minimum in the coke particles.

Fluid coking of residual petroleum oils isbeing caring of such petroleum residual oils contains ash constituentssuch as nickel, vanadium and other metals and sulfur which are undesirable constituents in coke and which are diflicultto remove because of the compact non-porous nature or structure of the fluid coke particles. While this compact structure is desirable from the standpoint of utilization in electrodes and the like,

it prevents removal of such contaminants by gaseous treating agents, extractants and the like. 7 v

Fluid coke particles from the fluid coking process are a different type of petroleum coke from petroleum cokes from other processes and have different characteristics. In the fluid coking process, coke particles are circulated between the reactor whe-re heavy petroleum oil is coked, and the burner where the coke particles are reheated by burning part of the coke particles. The heated coke particles are then recycled to the reactor where the particles have coke deposited on them by the cracking or coking reaction and are then heated to a higher temperature in the burner and this cycle is repeated many times to form spherical coke particles having layers in an onion-like formation or layer-on-layer formation or a shell within a shell structure.

Each fluid coke particle has a new layer of coke added or laid down as it passes through'the reactor and at the same time ash constituents and sulfur or sulfur compounds are laid down with the coke. As the coke particles pass through the burner vessel they are heated and have at least some of the volatile matter removed so that the coke particles are stronger and denser than coke obtained in other commercial coking processes. The removal of contaminants or undesirable constituents from the inner dense layers of the fluid coke particles presents a real problem.

According to the present invention, ash constituents or metal contaminants are substantially removed or the amount of such ash constituents or metal contaminants is substantially reduced in coke particles.

According to the present invention the amount of various ash and metal impurities in coke can be removed or substantially reduced by first coking a residual petroleum oil in the presence of a caustic material such as sodium carbonate, sodium hydroxide, or the like to form lo'wer boiling hydrocarbons and coke. The coke containing the caustic material is cooled and then leached with water containing nitric acid.

In the prior art it is known that coke containing a small amount of caustic material when leached with water alone will have some of the ash and metal contaminants removed but the extent of removal is of a much lesser degree than that obtained with the present invention.

Various extraction steps were tried in prior processes but the removal of metals or ash such as vanadium, nickel, iron, sulfur, etc., was negligible. Other processes pretreated the coke as by air oxidation to improve the porosity of the coke and while improved results were obtained the results were not entirely satisfactory because in many processes the coke product was burned.

In the present invention residual petroleum oil is coked at a temperature between about 900 F. and 980 F. About 3 to 12% by weight of solid sodium hydroxide per weight of residual oil was added to the oil before .coking. The co'ke produced was leached with a nitric acid solution having an acid concentration between about 4 and 12 wt. percent. Preferably, hot nitric acid at or near the boiling point is used. Instead of sodium hydroxide, other caustic material such as sodium car bonate may be used in about 3 to 12% by weight of the sodium carbonate per weight of residual oil.

Instead ofadding the caustic material to the residual oil as a solid, it can be added as a water solution and emulsified with the oil.

12% by Weight of the caustic material on the residual oil.

The fluid coke or other coke containing caustic material' was leached in one or more steps with a nitric acid solution and washed with water after each leaching step. At least 44% of the vanadium of the coke was removed'without any substantial loss of coke as is obtained in prior processes using a preoxidizing step, which if 'elfective, consumes about 25% of the coke.

The fluid coke particles from the coking step in the presence of caustic material contain caustic material on the coke. The caustic material may be sodium hydroxide or sodium carbonate either as pure or impure compounds, that is, these compounds need not be chemically pure.

lite, corresponding to 300 micron size.

ing an aqueous sodium hydroxide solution with residual petroleum oil having an initial boiling point of about 950 F. to give 5 wt. percent NaOH on the residual oil.

The residual oil-sodium hydroxide emulsion was coked by being introduced into a captive or fixed fluid bed. The fluid bed comprised 5300 grams of 44-55 mesh mul- The residual oil was emulsified with concentrated aqueous NaOH solution in the weight ratio of 1 part solution to 13 parts oil to give 5% NaOH on oil. This emulsion was fed for 180 minutes with 10% by weight of steam on the emulsion at a feed rate of about 28 cc. of emulsion per minute.

A the end of 180 minutes the oil-sodium hydroxide emulsion was cut out and steam was continued at the same rate. The temperature of the fluid bed during coking was 950 F. Coke was deposited on the mullite particles. The mullite particles were cooled in the bed and then removed from the bed. Then the mullite particles were tumbled and the coke skin or layer cracked off. The coke was separated from the mullite particles and about 660 grams of coke were produced. One portion of about pound was leached with hot water alone, and another portion of about A pound was leached with aqueous nitric acid solution, both at reflux conditions. The coke particles which were treated with the nitric acid solution were leached twice with nitric acid, first with about pound of a 15% by weight nitric acid solution at a temperature of about F. and then washed with water at ambient temperature.

The so-treated coke particles were then again leached with about pound of a 10% by weight nitric acid solution at about 190 F. and then again washed with A suflicient amount of a water solution of the caustic material is used to provide 3 to Leached With Leaehed With Hot Before Leaching Hot Water Nitric Acid Solution (Twice) V, p.p.m 3, 500 3,000 430 Fe, p.p.m 2, 000 1, 450 1, 080 Ni, p.p.m 500 460 125 From these data it will be apparent that the present invention is extremely effective in removing vanadium from fluid coke, as about 88% of the vanadium was removed. The invention is also effective in removing iron and nickel.

There was substantially no loss of coke in the leaching steps.

Additional work was done to cover petroleum oil residuum coked in the presence of sodium carbonate as well as sodium hydroxide, lower acid concentrations and a coke with a lower vanadium content.

In each case residual oil from Elk Basin crude, having an initial boiling point of about 850 to 1000" F., was mixed with solid sodium hydroxide in an amount to be equal to wt. percent on the residual oil feed, or mixed with solid sodium carbonate in an amount to be equal to 5 wt. percent on the residual oil feed.

The residual oil-caustic material in each case was destructively distilled at 1200 F. with a slow heat-up (about 12 hours to 1200 F.) in a programmed cal-rod furnace. The coke produced was cooled and then granulated to pass 65 mesh and refluxed with aqueous nitric acid solution at the boiling point using about 0.9 pound of solution to 0.1 pound of coke. The concentrations of the nitric acid solutions are given in the following table. The vanadium content of the coke from this residual feed is about 475 p.p.m.

The results are shown in the following table.

These data show the effective removal of vanadium and provide a process for producing a coke having less than 200 ppm. of vanadium which is the maximum concentration allowed by some aluminum companies for electrode coke. These data also show that a single 10% HNO leach is nearly equivalent to the successive 15% and 10% HNO leaches given in the Example I above. (72% vs. 88% vanadium removal.) Higher concentrations of HNO than 5% by weight HNO are preferred for more effective vanadium removal.

In these data, sodium carbonate gave superior results to sodium hydroxide when using 10% HNO aqueous solutions. (82% vs. 72% vanadium removal.

What is claimed is:

1. A process for producing fluid coke of reduced metals content which comprises mixing from about 3-12 Wt. percent of a caustic material selected from the group consisting of sodium hydroxide and sodium carbonate with residual petroleum oil having an initial boiling point above about 900 F., coking the mixture in a fluid bed at a temperature above about 900 F. to produce coke and vaporous hydrocarbons, cooling the coke, leaching the cooled coke with hot aqueous nitric acid having an acid concentration between about 4 and 12 wt. percent HNO and then water washing the leached coke.

2. A process according to claim 1 wherein the caustic material is used as'a solid or aqueous solution emulsified in the oil feed.

3. A process according to claim 1 wherein the coke is leached with a nitric acid solution, then water washed, then treated with a nitric acid solution again and then washed again.

4. A process according to claim 3 wherein the first nitric acid concentration is 5 wt. percent and the concentration of the second nitric acid solution is 10 wt. percent.

5. A process according to claim 1 wherein the temperature of the nitric acid solution is between about F. and 230 F.

6. A process according to claim 3 wherein the nitric acid treatments are carried out under refluxing conditions.

References Cited by the Examiner UNITED STATES PATENTS 3,179,584 4/1965 Hammer et al. 208-427 DELBERT E. GANTZ, Primary Examiner.

HERBERT LEVINE, Examiner.

Claims (1)

1. A PROCESS FOR PRODUCING FLUID COKE OF REDUCED METALS CONTENT WHICH COMPRISES MIXING FROM ABOUT 3-12 WT. PERCENT OF A CAUSTIC MATERIAL SELECTED FROM THE GROUP CONSISTING OF SODIUM HYDROXIDE AND SODIUM CARBONATE WITH RESIDUAL PETROLEUM OIL HAVING AN INITIAL BOILING POINT ABOVE ABOUT 900*F., COKING THE MIXTURE IN A FLUID BED AT A TEMPERATURE ABOVE ABOUT 900*F. TO PRODUCE COKE AND VAPOROUS HYDROCARBONS, COOLING THE COKE, LEACHING THE COOLED COKE WITH HOT AQUEOUS NITRIC ACID HAVING AN ACID CONCENTRATION BETWEEN ABOUT 4 AND 12 WT. PERCENT HNO3 AND THEN WATER WASHING THE LEACHED COKE.