US2104919A - Stabilized fuel oil - Google Patents

Description

Patented Jan. 11, 1938 UNITED STATES STABILIZED FUEL OIL Gary Myron Whitney, Compton, Califi, assignor to Shell Development Company, San Francisco, Calif., a. corporation of Delaware No Drawing. Application June 5, 1936, Serial No. 83,699

2 Claims.

This invention deals with stabilizing black fuel oils to prevent formation of sediment in storage.

Many black fuel oils produced by blending straight run components and cracked residues are known to have a tendency to'f-orm a carbonaceous sludge in storage. This tendency greatly lessens their value and usefulness, because it may result in plugging of fuel lines, spray lines and spray nozzles of burners, whereby burning may be interrupted. Various means which have been proposed to remove the sludge are of no avail in cases where the sludge is not originally present, but forms in storage.

It is the object of my invention to provide a product wherein the formation of sludge or sedimentation in storage of blended fuel oils of the type described containing deeply cracked residues, is prevented or at least retarded. My product consists essentially of a blend of the cracked residue with a straight run residue which has been subjected to an oxidation treatment prior to blending. To the blended fuel oil so produced other components may be added to adjust viscosity, flash, and other properties.

Stability of fuel oils toward sludge formation in storage has been estimated by a permanency test, in which a sample of a black fuel ,oil of known sediment content, as determined by A. SJT. M. method D-96-30, is exposed for 10 days in a closed container to a temperature of 93 to 95 0., after which period the sediment is again determined by the above A. S. T. M. method. The increase in sediment during the heating period is a goood indication as to how the fuel oil will behave on prolonged storage at atmospheric temperatures.

Another method of obtaining the indication as to the stability of a fuel more quickly, is to reflux the fuel at its normal atmospheric boiling point for a period of about one hour. An increase in the amount of B. S. & W. present after the heating period indicates the relative stability which may be expected of the fuel in storage. In practice a blended fuel oil containing a cracked residue of 4 A. P. I.-'7 A. P. I. gravity is considered sludge stable if its sludge content is not raised more than 25% of the original by the above described tests.

It is known that objectionable sludging is experienced mainly with blended fuel oils containing low A. P. I. gravity cracked residues, such as having gravities between about 4 A. P. I. 7' A. P. I. Particularly severe difiiculties are experienced when relatively thin and light gravity fuel oils are produced by diluting such heavy cracked residues, with relatively light gravity (such as from about A. P. I.-- A. P. I.) uncracked residual oils to produce easy-flowing fuel oils having gravities from about 10 A. P. I.- l8 A. P. I. The greater the dilution of the cracked residue, the greater usually is the danger I of producing a sludge-unstable blended fuel oil.

I have discovered, that the precipitation of sludge from the fuel oils produced by blending low A. P. I. gravity cracked residues with uncracked hydrocarbon oil residues can be inhibited by mildly oxidizing the latter prior to blending. My invention is particularly useful in preparing sludge stable blended fuel oils containing from about 10% to 80% heavy cracked residues.

The oxidation of the straight run residue or reduced crude, which is used for blending, may be carried out in any suitable manner, which may consist of blowing an excess of oxygen-containing gas, such as air, through the oil in a still at an elevated temperature preferably above 250 C. The upper practical temperature limit is determined by the volatility of the residue and should not exceed cracking temperature, i. e., about 400 C. It is also possible to carry out the oxidation by passing the oil, under superatmospheric pressure, if desired, through a heating coil and mix the oil with the air either before, and/ or during, and/or after the oil is passed through the coil.

I have found that the volatile products of oxidation which comprise water and organic acids may have a harmful effect on the permanency of blended fuel oils and, therefore, such oxidation products should be eliminated either during and/or subsequent to the oxidation treatment and prior to blending. While in most cases these compounds are carried away by the current of air as they are formed, in some instances a subsequent steaming or stripping may result in a marked improvement of the stabilizing power of the blown reduced crude.

The time of blowing necessary for successful stabilization varies inversely with the temperature, and also depends a great deal on the properties of the residue and the presence of oxidation catalysts, such as various heavy metals or their oxides, organic substances capable of forming peroxides under the conditions of blowing, etc. The proper blowing time for a given temperature must be ascertained experimentally for different types of fuels and may vary from about to 12 or more hours. If the blowing time is too short the stabilization, although improved, is incomplete and short of the optimum. On the other hand, if blowing is continued for too long a time, certain asphaltic components of the oil may become substantially insoluble in the oil and contribute to the instability of blended fuels produced with the overblown oil. In other words, the blown oil must itself be substantially storage stable.

While blowing of the straight run component of a blended fuel oil consisting of straight run and cracked residues has such a beneficial effect show no relation to behavior and practice.

on the stability of the blend, just the opposite is true when the cracked residue is blown.

This behavior of blended fuel [oils is particularly surprising inview of the known methods.

proposed for stabilizing asphaltic blends prepared from cracked residues. Oxidation or air blowing of such cracked residues either before or after blending them with an uncracked oil has been stated to produce stable asphalts entirely soluble in CS2 and C014. As explained hereinbefore, I

have discovered, that when the same treatment is applied to fuel oil blends, the resulting oils are sludge unstable. Therefore, it is essential in producing normally liquid fuel oil blends, as distinguished from asphalts, which are solid or semisolid at normal room temperatures (l5-25 C.), to oxidize the uncracked oil component in the absence of the cracked residue to be used for blending, and then blend the oxidized oil with such an. unoxidized cracked residue to produce a sludge stable fuel oil.

Differences between the behavior of fuel oils and asphalts may possibly be explained by taking intoconsideration the testing methods by which stability is established. It is generally acknowledged that testing methods, such as the aforementioned A. S. T. M. D-96-30, involving the use of benzol as a precipitant for the sediment in fuel oils, or the CS2 and C014 solubility tests for asphalts are purely arbitrary. Such tests have significance only if applied to that commodity for which they have been designed. They have been adopted only because they show a reasonable relationship to the behavior of the respective com.- modity in actual use. Thus, if a fuel oil stability test is applied to asphalts, or an asphalt test is applied to fuel oils, results are obtained which From this it must be concluded that stability of fuel oils against sludging and stability of asphalts against separation, are two entirely different propcities, which must be evaluated by specific noninterchangeable tests. Therefore, when speaking in this application and in the appended claims of stability or permanency of fuel oils, it shall be understood that itis referred to stability and permanency solely as measured by the tests hereinbefore. described.

The following illustrative examples clearly show the advantages and limitations of my treatment. A fuel oil prepared by blending 65% of a cracked residue, 28% of a straight run residue and 7% of a distillate oil had an original sediment content of 2% and an instability of 3.2%. A similar blend produced after blowing the straight runcompon'ent with air for 4%; hours at 325 C., after dilution with a small additional amount of distillate oil to match the viscosity of the first blend, had an instability of -.2%. During the blowing, low-boiling vapors including water were continuously withdrawn.

In a second blowing test, the low-boiling vapors, including water, were continuously returned to the oil, and the blend produced with the resulting blown oil showed a precipitation of 4.5%, which is poorer than the stability of the first blend.

Blowing of the cracked component instead of the straight run component not only failed to have a beneficial effect, but was quite detrimental. The cracked component of the first example was blown for only hour at 325 C., whereupon the fuels, respectively, by themselves.

stance of blowing the blend of the first example instability of the blend rose to 7.2%. Blowing the blended fuel usually results in an efiect which is between the extremes of benefit and detriment attributable to blowing the straight run or cracked In the infuel oils, it appears that the oil-soluble products of oxidation formed by the mild oxidation of the straight run fuel oil, being of colloidal size, possess the property of acting as protective colloids for components contained in cracked residues, which components tend to be precipitated upon blending with straight run hydrocarbons. It appears that blowing of cracked residues leads almost immediately to the formation of polymers which are substantially insoluble in straight run hydrocarbons, and upon blending a cracked blown residue with straight run hydrocarbons of the type contained in fuel oils, the polymers are precipitated and form a sludge. l

The effect of low-boiling products of oxida tion on permanency, which has been described as being harmful, is probably that of a coagulant. Acids are frequently capable of coagulating colloidal dispersions, and the small quantities of volatile organic acids formed during oxidation appear to be sufficient to cause in many instances the coagulation of colloidally dispersed particles. Where the protective action of asphaltenes is very pronounced, coagulation may be prevented in spite of the presence of volatile products of oxidation.

Acidic components contained in the oxidant may have a'coagulating effect similar to that of the volatile products of oxidation. For instance if mere traces of sulfur dioxide, hydrochloric acid or other acid fumes are contained in the air used for blowing, the blowing of the straight run oil may have a harmful rather than a beneficial effect on the permanency of blended fuels of the type herein described.

I claim as my invention:

1. A blended non-sludging low-viscosity fuel oil having a gravity from 10 A. P. I. to 18 A. P. I. consisting of a cracked residuum having a gravity from 4 A. P. I. to 7 A. P. I. containing components which upon blending with an unoxidized straight run mineral oil form a carbonaceous sludge and an oxidized straight run residual fuel oil having a gravity from about A. P. I. to 25 A. P. I. before oxidation containing a sludgeprotective colloid formed by the mild oxidation of said straight run residual fuel oils.

2. A blended non-sludging low-viscosity fuel oil having a gravity from 10 A. P. I. to 18 A. P. I. consisting of a cracked residuum having a gravity from 4 A. P. I. to 7 A. P. I. containing components which upon blending with an unoxidized straight run mineral oil form a carbonaceous sludge, an oxidized straight run residual fuel oil having a gravity from about 15 A. P. I. to 25 A. P. I. before oxidation containing a sludgeprotective colloid formed by the mild oxidation of said straight run residual fuel oil and a lowviscosity distillate oil.

GARY MYRON WHITNEY.