US2065281A - Process of improving mineral oils containing lime - Google Patents

Description

Dec. 22, 1936. A. J. KRAEMER 2,065,281

PROCESS OF IMPRO VING MINERAL OILS CONTAINING LIME Filed May 4, 1955 Ac: 9 OIL SUPPLY CQACKING STI LL SETTLJ N6 012 STOZAGE- TANK Gum/M44 Patented Dec. 22, 1936 UNITED STATES PATENT OFFICE Albert J. Kraemer, Washington, D. 0.

Application May 4,

1 Claim.

This invention relates to the improvement of products of petroleum refining which have objectionable properties, and more particularly to the improvement of residual fuel oils or other re- 5 sidual products of distillation or cracking which contain lime or other compounds which upon combustion of the. oils yield alkaline solids, by the use of substantially valueless by-products of petroleum refining.

The principal object of the present invention is to improve residual fuel oils or other residual products of distillation or cracking which contain lime or other compounds which upon combustion of the oils yield alkaline solids, and at the same time make advantageous use of the socalled acid sludge or the constituents thereof known as acid oil and acid tar, all of which are substantially valueless by-products of petroleum refining.

Other objects and advantages of the present invention will become apparent during the course of the following description.

As is well known, the usual practice of refining crude petroleum includes treating it in distilling and/or cracking equipment. As a result, a large proportion of the petroleum employed as charging stock for the still or cracking unit is converted into a distillate which is separately recovered. A small quantity, varying from less than 1 per cent. to more than 10 per cent., of the charging stock is converted into gas and coke. The remaining product of distillation or cracking is a heavy oil which is commonly designated as the residuum, which product is widely used as fuel for burners of industrial heating and power plants and for other purposes.

As will be apparent, any solid, non-volatile material present in the charging stock or formed during the passage of the stock through the still or cracking unit will be concentrated in the liquid residuum and the coke, as it obviously will not be vaporized during the distillation or cracking and pass off with the distillate and the gas. Thus, the fuel oils or other residual products of cracking or distillation will contain a portion of the suspended solids which were present in the charging stock or formed during the distillation or cracking thereof. However, except in cases where certain chemical treating agents have been added to the charging stock, the percentage of incombustible solids in residual oils is ordinarily small and these solids are substantially inert, with the result that the fuel oil is not detrimentally affected to any substantial extent as a result of their presence therein.

1935, Serial No. 19,905

However, in recent years petroleum refiners have made a practice of adding lime to crude petroleum or other charging stock before the material enters the still and/or cracking equipment. One object in adding lime is to reduce the corrosiveness of the crude petroleum or other charging stock due to the hydrogen sulfide or other acidic compounds present in the charging stock or formed within the distilling or cracking equipment under the conditions that obtain with in the equipment. Another object of adding lime tothe charging stock is pointed out by S. P. Armsby in Refiner and Natural Gasoline Manufacturer, July, 1932, page 415, where it is stated that cracking still coke is well known to be much more easily broken up and removed from the still if lime has been added to the charging stock. It is further pointed out by Armsby that part of the lime is carried over to the settling tank where it acts both mechanically and chemically to cause better separation and faster settling of the B. S. The sediment tends to become more granular and less sticky; it solidifies more quickly and is easier to handle.

Quite frequently, relatively large amounts of lime are added to crude petroleum or other charging stock prior to the treatment thereof in the distillation or cracking equipment. For example, in an article in Oil and Gas Journal, June 5, 1930, beginning at page 35, W. F. Ziegenhain points out that before charging a particular crude oil to the topping stills, an average of 0.456 lb. of lime per barrel is customarily mixed therewith. Also, W. G. Whitman and J. K. Roberts in the Bulletin of the American Petroleum Institute, Vol. XI, No. I, January 2, 1930, page 151, state that for a Holmes-Manley charging stock containing 0.25 per cent. sulfur, approximately 1.0 lb. of hydrated lime was added per 100 gallons of cold feed. In the same paper the authors also report the experience at another refinery where a virgin stock containing 1.1 per cent. of total sulfur required 1.7 lb. of lime per 100 gallons of feed, and a cycle stock containing 0.93 per cent. sulfur required 0.75 lb. of lime per 100 gallons of feed. In making a general summary relative to the use of lime in charging stock, Whitman and Roberts make the following statement:

Reports from various companies which have used lime show that concentrations from 0.1 to as high as 10 lbs. (of lime) per barrel have been employed on a plant scale. In general, however, the average amount used is in the neighborhood of 1 to 2 lbs. of hydrate (of lime) per 100 gallons of cold feed.

As will be apparent, the use of such relatively large proportions of lime in treating charging stock prior to passing the same through cracking or distillation equipment will result in the presence of a relatively large percentage of suspended lime and other calcium compounds in the residua1 oil. For example, let it be assumed that a charging stock upon distillation or cracking will be converted into '75 per cent. by volume of distillate, 15 per cent. of liquid residuum, and 10 per cent. of coke and gas. Let it be further assumed that lb. of hydrated lime is added per barrel of charging stock. According to the paper of Whitman and Roberts previously cited, the ultimate disposition of the lime added to the charging stock is about one-third in the coke and twothirds in the liquid residuum. Since the distillate constitutes 75 per cent. of the charge, 4 barrels of charge will yield 3 barrels of distillate and 0.6 barrel of liquid residuum, with the remainder of the charge accounted for as coke and gas. The 0.6 barrel of liquid residuum will contain of the 2 lbs. of hydrated lime that was added to the 4 barrels of charging stock, the lime occurring mainly in the form of calcium salts of acidic compounds, mostly sulfur compounds, which yield alkaline solids upon combustion of the residuum containing the same. Since 0.6 barrel of residuum will contain 1 lbs. of lime and lime compounds, a barrel of residuum will contain 2.2 lbs. of the same.

The presence of such relatively large percentages of solid calcium compounds in the liquid residue products of cracking and distillation has created a serious problem, the importance of which has been recognized in the art. For example, J. I. Dickinson in The Petroleum Engineer, Midyear, 1930, page 198, says:

When fuel containing the lime is burned, the lime collects as a dust on the tubes and in the flues, where it acts as an insulator, preventing proper heat transfer. In some cases the lime also tends to flux the fire-box linings unless special materials are used to resist such action.

In the paper of Whitman and Roberts, pre viously cited, it is stated:

The ultimate disposition of the lime fed to a Holmes-Manley unit is about one-third in the coke and two-thirds in the tar. Evidently the presence of so much lime in the tar may make it unsalable for certain purposes, thus introducing the problem of removing it by filtration or other means. In some cases, this problem has been regarded as sufliciently serious to preclude the use of lime entirely, although several refiners have achieved a successful solution.

Ziegenhain, in the article previously cited, states at page 333 that when residuums containing lime are burned as fuel a fiuify deposit of calcium sulphide or sulphate collects on top of the tubes in the convection section of the pipe stills, which deposit must be removed about every 10 days.

As will be apparent from the foregoing, the use of lime in treating crude petroleum or other charging stock prior to distillation or cracking is quite widespread, it being estimated conservatively that lime is added to millions of barrels of crude petroleum and other charging stocks annually. It is further evident from the foregoing that the presence in residual oils of lime and reaction products thereof with constituents of the oils is seriously objectionable. Therefore, the industry is confronted with the problem of retaining the advantage of the use of lime in charging stocks while avoiding the disadvantage of having the lime and other calcium compounds present in the liquid residues remaining after the cracking and/or distillation of such charging stocks.

As indicated above, in order that the disadvantages resulting from the presence of lime and other calcium compound in fuel oils and other residual products may be overcome, it is necessary either that such calcium compounds be re moved from the oils prior to combustion thereof or that the calcium compounds be rendered inert so that upon the combustion of the oil there will not be produced alkaline solids which will tend to flux firebox linings or otherwise detrimentally affect oil burners or boilers. In view of the difficulty and expense incident to the removal of the lime and other calcium compounds from the residual oils prior to combustion thereof, this possible method of solving the problem is not practical from a commercial standpoint. Therefore, it results that the problem must be solved by the renderingof the calcium compounds inert.

It might appear that the rendering inert of the calcium compounds present in residual oils might be effected in a practical way by the treatment of the residual oils with acids or other compounds such as suitable salts which would react with the calcium compounds present to render them inert and harmless upon the combustion of the oil containing, the same. However, the use of such chemical treating agents for the purpose specified is a practical impossibility from a commercial standpoint. In the first place, the price obtainable for residual oils is such that too great an increase in production costs would result from the purpose and use of chemical reagents of the character referred to for treating such oils. In the second place, the use of chemical treating agents of the character referred to would produce only partial results, if any. For example, if the residual oils containing lime and other calcium compounds were treated with anhydrous acids, such as concentrated sulfuric acid, for example, the acids would react with constituents of the oils before neutralizing the lime or rendering inert the other calcium compounds present. If, instead of using anhydrous acids, there were employed acids in such dilute aqueous solution that constituents of the oil would not be acted upon thereby, and the acid constituents present would be available to react upon the lime and other calcium compounds, there would be introduced into the oil an amount of water far beyond the permissible limit, which in commercial practice is about 2 per cent. by volume.

If instead of using acids, certain salts might be found suitable for use, it would be necessary to add the salts in solid form in order to avoid introducing water beyond the permissible limit, and by the use of the salts in solid form sumciently intimate contact with the lime and other calcium compounds could not be obtained in commercial operation to bring about the desired results.

So far as I am aware, the problem of overcoming the disadvantages of the presence in residual oils of lime and other calcium compounds has not been overcome and, in some instances, as indicated in the paper of Whitman and Roberts cited above, refiners have found it necessary to avoid the use of lime in treating charging stocks in order to eliminate the disadvantages resulting therefrom.

I have discovered that the disadvantages hithertoencoiint'ered as a result of the presence of alkalinecompounds or non-inert reaction products thereof in mineral oils, such as residual oils from cracking or distilling charging stocks containing A lime, can be avoided, without the introduction of the element of substantially increased expense, by treating such oils with an acidic by-product of petroleum refining which is not only substantially valueless but which frequently must be disposed of as a waste product. Specifically, the desired results are obtained by adding to the oil to be treated either the so-called acid sludge produced in the refining operations customarily used, or acid oil or acid tar derived therefrom.

.As is Well known, the treatment of petroleum with concentrated sulfuric acid is one of the most widely used refining operations. As a result of this treatment, a viscous sludge is formed, called acid sludge, which is a complex mixture of sulfuric acid, compounds originally present in the petroleum fraction and products of reaction between the acid and the oil.

Acid sludge presents a problem in its disposal. While numerous methods have been proposed for treating acid sludge and improving the utilization of the by-products, the most common method of disposal is to treat the acid sludge with water or steam, which results in breaking the sludge into three layers. The upper layer is commonly known as acid oil and is composed largely of products of hydrolysis. The middle layer is a dilute solution of sulfuric acid in water, which solution is customarily concentrated into strong sulfuric acid and reused. The bottom layer, commonly called acid tar is a carbonaceous material of indefinite composition and contains some sulfuric acid and/or compounds having a strong acid reaction. While, as stated, the middle layer, consisting of a dilute solution of sulfuric acid, has a commercial value, the upper layer of acid oil and the lower layer of acid tar have no important commercial value.

I have discovered that acid sludge itself or the acid tar layer or the acid oil layer may be advantageously disposed of by mixing the same with residual oils containing lime and other calcium compounds. As a result of such treatment the lime and other objectionable calcium-compounds present in the oils are rendered inert so that alkaline solids are not present upon combustion of the oils. Not only is an alkaline oil of the type under consideration capable of being rendered substantially neutral by the addition thereto of acid sludge or acid oil or acid tar, but other important commercial results are also obtained from the treatment. In the first place, the nonacidic constituents of the acid sludge or acid oil and acid tar, which are otherwise substantially valueless, serve to increase the volume of the residual oil treated therewith without detrimentally affecting the residual oil. In fact, improvement of the residual oil will be obtained in some cases by the treatment of the same with the acidic reagent used, particularly where such reagent is acid oil. In the second place, the treatment of the residual oil with acid sludge, acid oil or acid tar greatly facilitates the settling out of the suspended solids during the usual settling operation. As a result of the treatment the lime or calcium compounds held in suspension in the residual oil will be converted into calcium sulfate, which will tend to settle out more readily because of its greater specific gravity. The specific gravity of calcium hydroxide is given in Van Nostrands Chemical Annual as 2.078, whereas the specific gravity of calcium sulfate is given as 2.964, an increase of more than 40 per cent. in specific gravity. As a result of this increase in specific gravity by the treatment of residual oils with acid sludge, acid oil or acid tar, the solid reaction products which are formed as a result of the treatment will largely settle out during the usual treatment of the oil in the conventional settling tank to which the residual oil is customarily discharged from the still or cracking unit. If the residual oil is passed directly to a storage tank, substantial settling will take place in such tank. However, even if there is no substantial removal of the solid reaction products by settling out, the solids remaining in the oil will not be found seriously objectionable in view of the inertness thereof.

In treating the alkaline residual oil containing the solids which are to be rendered inert,

sufficient acid sludge and/or acid oil and/or acid 1 tar should be employed to produce a resulting mixture which is substantially neutral. Of course, the amount of acid sludge and/or acid oil and/or acid tar to be added toa given alkaline oil will depend upon the degree of alkalinity of the oil and also upon the degree of acidity of the treating reagent or reagents added. However, the proper relative amounts to be employed in any particular case can be readily determined by testing the alkalinity of the oil to be treated and the acidity of the treating reagent and computing the proper amount of treating reagent to be used by simple stoichiometrical calculation.

In preferred practice, the acid sludge and/or acid oil and/or acid tar should be added to the residuum containing lime at the point where the residuum leaves the still at an elevated temperature, on its way to the settling or storage tank. Introducing the treating reagent at this point will permit intimate mixing of the two materials at a high temperature in the pipe line under turbulent flow. Any reaction that has not been completed by the time the mixture reaches the settling or storage tank will be completed in a short time in the tank. The turbulent flow in the pipe line will cause the solid material to remain in suspension until the turbulence is checked in the settling or storage tank, whereupon the solid material will settle out relatively rapidly. Of course, the treating reagent may be added to the residual oil at a point other than that indicated above, as in the storage tank, for example, but I prefer to introduce it at the point indicated.

In the accompanying drawing I have shown in diagrammatic form an assembly of apparatus suitable for use in the practice of my present invention.

Referring to the accompanying drawing, the numeral I0 designates a still or cracking apparatus provided with a valved inlet pipe I l for the introduction of charging stock, an outlet pipe l2 for the discharge of distillates, and an outlet pipe l3 for the discharge of the residuum from the still or cracking apparatus. The outlet pipe i3 is connected at the T M with a pipe I 5 through which the residuum is discharged into a settling or storage tank I 6 which is provided with a valved outlet pipe IT. The acid oil with which the residuum is to be treated is discharged from a container H3 or other source of supply through a, pipe I9 which is connected with the pipe I5 at the T M. As stated above, the acid oil is preferably added to the residuum during the passage thereof from the still or cracking apparatus I 0 to the 7 settling or storage tank l6 since this permits the intimate mixing of the acid oil and the residuum at a high temperature and under conditions of turbulent flow.

As will be apparent from the foregoing, the present invention results in the improvement of two products of petroleum refining which have objectionable properties. As a result of the pres ent invention, petroleum products containing lime or other compounds which yield alkaline solids upon combustion of such products are improved and acid sludge and/or constituents thereof which are substantially valueless are rendered commercially useful. An important advantage of the invention lies in the fact that the advantages are obtained without involving any substantial expense.

While I have described in detail the preferred practice of my invention it is to be understood that the details of procedure may be variously modified without departing from the spirit of the invention or the scope of the subjoined claim.

I claim:

In the refining of petroleum wherein a charging stock to which lime has been added is treated in a distillation or cracking apparatus from which a residuum at elevated temperature is discharged to a settling or storage tank, said residuum containing calcium compounds resulting from said addition of lime to the charging stock, the improvement which comprises adding to said residuum, during its passage from said apparatus to said tank, acid oil separated from acid sludge in substantially the amount required for reaction with said calcium compounds to render the calcium compounds inert and to increase their specific gravity to expedite their settling out of the residuum.

ALBERT J. KRAEMER.

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