US2131879A - Method of treating hydrocarbon distillates - Google Patents

Description

Patented Oct. 4, 1938 ware nm'rnon or TREATING nrnaoosanon ms'rmm'rss Waldo can: and Carroll '5. Hochwalt, Dayton,

Ohio, assignors to Monsanto Chemical Company, St. Louis, Mo., a corporation of Dela- No Drawing. Application March 3, 1936, Serial No. 66,893

3 Claims. (01. 196-36) This invention relates to the refining of petroleum distillates for motor fuel purposeswhich are rich in impuritiesthat impart color ,and odor, or are productive of gum. In addition, the inven- 5 tion contemplates a treatment whereby the antiknock .value of the fuel is increased and the susceptibility to tetra ethyl lead is improved.

The petroleum fractions which may be treated according to the present invention are generally made by cracking relatively higher boiling petroleum products. However, they may also be produced by polymerizing lower boiling products. In either case the raw material having the desired boiling range for motor fuel purposes may be 7 malodorous, 011' color, rich in gum forming con stituents, and'may frequently contain sulfur in objectionable amounts.

Various methods are now used to refine this,

so called, raw gasoline to render it suitable for- 2 motor fuel purposes. In most instances several successive treatments are necessary in order that a product having the desired properties is ultimately obtained. One common procedure for removing the sulfur and gum forming constituents consists in washing the raw gasoline with sulfuric acid, subsequently with water, and thereafter with alkali to remove residual acidity. The product is then redistilled.

An alternative procedure consists in contacting the raw gasoline with active clay, whereby the gum forming constituents are partially separated. It is generally necessary to follow the clay treatment with a doctor treatment, which is calculated to remove objectionable odors, especially those attributable to the presence of sulfur impurities; Not infrequently this is also necessary in the case of acid treated gasoline. With either method of treatment gum inhibitors are commonly added to the gasoline, especially if the gasoline is apt to-be stored for. a considerable period of time before use.

Present day practices share many objectionable features. Thus, for example, the sulfuric acid treatment is not selective. In other words,

it not only combines with the gum forming constituents, but also with the desirable oleiinic components of a raw gasoline, thereby reducing the yield of gasoline and impairing the antiknock quality of the product. A reduction in the amount of sulfuric acid employed to reduce the loss of desirable motor fuel constituents is possible only to a limited extent inasmuch as a substantial amount of sulfuric acid is necessary,

especially where a reduction in the sulfur content of the gasoline is desired. Because it is not possible to improve gasoline with regard to the presence of sulfur and gum forming constituents without materially reducing the yield and antiknock properties of the fuel, refiners indulge in l 0 a compromisebetween gum andsulfur impurities on the one hand and cost of refining reagentsand sacrifice in yield on the other. Thus, for example, a treatment with sulfuric acid may lower the antiknock value of the fuel 5 to 15 points if a substantially gum free and low sulfur product is desired. At the same time ten per cent or more of the fuel may be lost as sludge.

The clay treatment avoids certain objectionable features of the sulfuric acid treatment, but has no effect whatever on sulfur. Furthermore, the clay treatment does not eliminate the gum forming constituents entirely, but rather eliminates only part of these to give temporary stability and necessitates the use of so-called gum.

inhibitors in the finished gasoline product to attain relatively permanent stability.

Whether one employs the clay or acid treatments, it is generally necessary, in order to obtain a gasoline product having the required color stability and freedom from odor, to subject it to a sweetening treatment. This treatment requires the use of additional chemical reagents and necessitates several additional steps in the refining operation.

In the usual sweetening reaction, the mercaptans are transformed quantitatively to disulfldes. This is usually accomplished with the aid of a source of oxygen. The presence of smallquantitles of disulfides contributes materially to poor color stability. poor susceptibility to the effect of tetra ethyl lead, poor susceptibility to gum inhibitors, and'to an actual loss in octane number. In addition, the presence of free sulfur, which is normally required in excess to assure complete conversion of the mercaptides to disuliides, impairs color stability and promotes corrosion. The efleot of oxygen on cracked gasolines is rather well known, and the resulting peroxidation exerts a detrimental effect on inhibitor susceptibility and antiknock properties, (see Oil and Gas J ournal" of February 6, 1936, page 28 et seq.)

According to the present invention, the raw gasoline is treated in a manner described more fully hereinafter, whereby the following advantages and improvements over the prior processes are attained:

1. Practically complete and selective removal-of gum forming constituents, without loss of desirable gasoline constituents.

2. Saving in cost of gum inhibitors, by eliminating the necessity therefor.

3. Improved antiknock properties.

4. No-loss in the desired olefin or aromatic consteps.

9. Recovery of gum and sulfur components in a non-corrosive utilizable form.

10. General applicability of refining ,method to widely varying raw gasolines whereby a product having a high induction period is readily and conveniently obtained.

According to one preferred embodiment of the present invention, petroleum hydrocarbon vapors of the gasoline boiling range and steam are contacted with a solid catalyst surface or are scrubbed with a mobile liquid catalyst medium, the temperature, time of contact and activity of the catalyst being so adjusted with respect to each other as to convert practically all of the gum forming constituents and a substantial part of the sulfur impurities into relatively high boiling polymers. In general, the preferred catalytic materials are nonreducible, substantially non-volatile, inorganic acids, or acid reacting salts, or esters, which may include activating substances, notably salts of heavy metals. By means of the foregoing treatment the undesirable impurities are converted into a form whereby they may be separated by various physical means that do not necessitate the use of chemical refining agents.

The following comparative analyses of a gasoline before and after treatment are typical of the results obtainable by practicing our invention:

We are aware that it has been proposed heretofore to treat various hydrocarbons with mixtures of phosphoric acid and sulfuric acid. However, we have found that under the conditions of our process in its preferred form sulfuric acid is rapidly decomposed. Furthermore, the various acids of phosphorus have been considered ineffective in and of themselves for the purpose or refining raw gasoline (U. S. P. 1,914,953), and to the best of our knowledge the use of these acids has met with no commercial success in this field. We are also aware that it has been proposed heretofore to pass hydrocarbon vapors in admixture with steam over a carrier sprayed with phosphoric acid. However, such a process is not efiectlve, or only partially effective, at best and is supplemented by a chemical consuming refining step, such for example, as a hypochlorite treatment (U. S. P. 1,709,315).

We have found that the presence of steam does not necessarily prevent the complete removal of the undesirable impurities, particularly the gum forming constituents, and that by proceeding as hereinafter more fullyset forth, it is entirely possible to obtain all of the advantages of the invention as enumerated hereinabove, without resorting to such supplementary chemical refining We have discovered that even in the pres: ence of steam the conversion of the objectionable constituents to higher boiling products is complete, but because of the presence of steam, these higher boiling polymerized products are carried over with the gasoline vapor, and when the gasoline vapor has condensed, reappear in the liquid product. Further, we have found that if the water is removed from the condensate as by decantationand the gasoline is redistilled in the absence of the steam, a product of excellent quality is obtained.

The polymerized products which are carried along with the treated gasoline vapors and steam may be removed in other ways, for example, by drying the vapors as with calcium oxide, or other suitable drying agents. In this way the water is removed and the polymer may be separated from the gasonline vapors by suitably adjusting the temperature, the polymer thereby condensing out because of its lower vapor pressure. Alternatively, the polymer can be removed from the steam containing gasoline vapor stream by scrubbing the vapors with high boiling liquid media capable of holding back the polymer, such for example, as phosphoric acid, lubricating oil, molten paraflln, and other scrubbing media having a solvent action or aflinity' for the polymers formed in the catalytic step of our refining process.

In our co-pending application filed of even date, we have shown that if a substantially water-free gasoline vapor is treated with various catalytic compositions, such as are described more fully hereinafter, the step for removing the polymer is unnecessary and a product having excellent gasoline motor fuel properties is directly obtainable. By way of illustration:

A commercial cracked gasoline was treated by flash distilling the the raw gasoline at a rate of 200-300 c. c. per hour in such manner that throughout the run, vapors of substantially uniform composition were obtained which were at a temperature of approximately 175-185 C. These vapors were introduced through a quarter inch tube into phosphoric acid of approximately concentration and allowed to bubble upwardly through about 6 to 10 inches of the acid which was maintained at approximately -180 C. by an oil bath that surrounded all except a small portion of the upper extremity of the catalyst containing vessel. Sufllcient reflux was thus afforded in relation to the temperature, acid concentration, etc. to produce a clean separation of gum forming constituents and substantial separation of sulfur containing constituents in the form of a relatively high boiling polymer, which polymer was all retained in the catalyst containing vessel and in intimate admixture with the catalyst. This intimate mixture of polymer and catalyst was found to be at least as good a scrubbing mediumfor the purpose of our invention as the acid itself.

Following condensation of the scrubbed vapors,

a light aqueous alkali wash was used to remove the traces of hydrogen sulfide. The following were the characteristics of the original and the treated gasoline:

The oily polymer was formed in the phosphoric acid to the extent of about 1% of the weight of the gasoline treated. This polymer upon subsequent distillation at atmospheric pressure possessed a boiling range of 240-330 C.; only a small undistilled'residue remained. During operation of the process the polymer was disseminated throughout the acid in the form of tiny globules by the flow of gasoline vapors through the liquid Treated and redistilled Gum value (cu. dish) 384 4 Sulfur perwnt 0. l6 0. l2 Bromine numbcnr..- 63. 2 57. 4 Oxygen bomb stability 1 hour 4.5 hours mixture. Upon stopping the flow oi. vapors through the catalyst the liquid polymer rose rapidly to the surface of the acid and was thereupon separated from the acid by decantation in a substantially acid free condition. The acid layer was thus recovered practically quantitatively and in excellent condition for repeated use.

The present invention contemplates the adaptation of the process of our co-pending application to a gasoline vapor mixture which contains steam. As indicated above, when such a. vapor mixture is subjected to the action of our catalysts a gum free condensate is not obtained directly.v

The following examples are illustrative of our invention when steam or water are present in the treating system:

Example I A commercial cracked gasoline was treated by flash distilling the raw gasoline at a rate of 200-300 c. e. per hour in suchhmanner that throughout the run, vaporsof substantially uniform composition were obtained which were at a temperature of approximately 17 5-185 C. These vapors were introduced througha quarter inch tube into phosphoric acid of approximately 75% concentration and allowed to bubble upwardly through about 6 to 10 inches of the acid which was maintained at approximately l70- -1 i i0 C. by an oil bath that surrounded all except, a. small portion of the upper extremity of' the catalyst containing vessel.

The discharged gasoline vapors contain water which had its source in the dilute acid being used as a catalyst. Following condensation, the water was allowed to settle, the clear supernatant gasoline layer was decanted. After a mild aqueous 'These results show that although under certain conditions the gasoline obtained isnot free of gum, nevertheless, the gum forming constituehts are converted into such form as to be readily separable from the gasoline by physical means, as for example, simple distillation.

Example 11 A commercial cracked gasoline was'treatedby flash distilling the raw gasoliiie at a rate .of

200-300 0. c. per hourin such a manner that throughout the run vaporsoi substantially uni form composition were'obtained which were ata temperature ofapproximately l' l5-l8 5 C. Along with the gasoline vapors steam was introduced" in a quantity equivalent to about 2 or 3' per cent of the gasoline being treated. These vapors were introduced through a quarter inch tube into phosphoric acid of approximately 85% conc'entration and allowed to bubble upwardly through about 6 to 10 inches of the acid which was maintained at approximately 170-180 C. by an oil bath that surrounded all except a small portion of the upper extremity of the catalyst containing vessel.

The'resulting gasoline vapors were conducted through a lagged tube 2 inches in diameter and 1 foot long, packed with granular lime (CaO). After contacting these vapors with the lime they were led to a condenser. The condensed gasoline was of a bright, water white appearance and had characteristics similar to those given in Example I. v

Example III The procedure in this embodiment was the same as in Example 11 with the exception that instead of passing the vapors over lime, they were introduced into a bath of molten paraflln which was,

Example IV Substitute 100 per cent phosphoric acid and otherwise proceed as in Example 2. Equilibrium acid condensation conditions are soon established and the product obtained after a period of 2 or 3 hours will be found to be substantially identical with that obtained according to Example II.

Example V To illustrate the' application of the principles or ur invention -to a. process in which the gasoline is'in vapor state and the catalyst is solid rather" than fluid or mobile, as in the case of the preceding examples, the gasoline vapor-steam mixture, as described in Example II, was passed through a tube or tower filled with granules of pumice stone which were saturated with phosphoric acid. The temperature of the tower was preferably adjusted at 200-215 C. to prevent substantial condensation of the polymer. The tower consisted of a2 inch glass tube 30 inches Iongflagged and electrically heated to maintain the desired temperature condition. Some condehsation was perceptible but it did not interfere with the successful working of the process. In lieu 'oi'lthe pumice granules there were substituted granular pellets of clay made by mixing clay withapproximately 25 per cent by weight of 85 per cent phosphoric acid and sufliclent water to produce a'moldable mix. The mix was formed into pellets and dried at 105 C., after which it wasp'acked in the tower.

Other carriers may be used, such for example as. a moldable mixture of sodium meta phosphate and phosphoric acid together with activated carhonor other adsorbi-z'nt;v forms of carbonaceous materials capable of holding .the phosphoric acid. Coal, coke, peat and cellulosic materials may be substituted for the activated carbon to form a'soil carrier for the active component.

The vapors were introduced at the top of the tower and caused'to flow downward through the catalyst after which they were condensed and worked up as in. Example 1,- Example 11 or Example III t0v obtaimtheflnishedproduct.

While ,ortho' phosphoric acid is admirably suited for the purpose of our process, in that it not only effects substantially complete conversion of the gum forming constituents into separable form, but in addition attains theother desirable objectives of the present invention, nevertheless other catalytic compositions may be substituted therefor. Thus, for example, a mixture of the pyro and ortho phosphoric acids may be employed, or alternatively a mixture of the meta, pyro and ortho phosphoric acids. In lieu of phosphoric acids the corresponding phosphorous, and hypophosphorous acids may be substituted in whole or in part for the phosphoric acids. In the case of the acids of lower state of oxidation there is evidence that the materials react, at least in part, to form the more stable phosphoric acid with attending formation of phosphine.

In addition to the oxygen acids of phosphorus. one may use the acid salts to replace the free acid in whole or in part. Similarly one may substitute the alkyl or aryl acid esters, which evidently likewise undergo some chemical change in the course of their use, but as in the other instances, the reaction products are themselves catalytically active.

While from the standpoint of availability, the oxygen acids of phosphorus and their derivatives are especially suitable, we may use other known non-reducible acids of phosphorus, such, for example, as the sulfur containing acids of phosphorus or the sulfur and oxygen containing acids of phosphorus, as for example, the thiophosphoric acid HaPSOa, or dithiophosphoric acid.

The catalyst may be made in various ways, for .example, one may use ordinary phosphoric acid syrup of commerce, which is approximately per cent H3P04. However, if desired, one may use percent H3PO4 by adding sufficient P205 to the phosphoric acid syrup of commerce to combine with the free water. An excess of P205 may be added to the phosphoric acid syrup over and above that required to react with all of the water to form 100 per cent H3PO4, in which case one obtains a mixture of the pyro and ortho phosphoric acid, or depending upon the amount of P205 added, a mixture of all three of the phosphoric acids. Instead of adding .PzOs to the commercial phosphoric acid, one may add P203.

The composition of the starting catalytic material may be varied considerably inasmuch as it undergoes some change with use in attaining an equilibrium. This is particularly true with respect to the water content of the catalytic composition. 4

While we prefer to use a catalytic composition which is immiscible with the polymer, whereby it may be separated from the accumulated polymer by stratiflcation and decantation or draining, it is to be understood that the catalyst can be present as a solid, in which case it may be suspended or dispersed in the polymer or some other fluid inert vehicle.

As indica d in Example V the various catalysts may consist of stationary solid fragments saturated with or consisting in part of the catalytic compositions.

A further modification of the catalytic compo,- sition consists in the use of catalytically active saltseither alone or in admixture with the free acids which salts exert desirable'catalytic influences. Such effect is produced by the addition of salts of catalytically active metals, such as copper, nickel, cadmium, zinc, cobalt, chromium, iron and other heavy metals. For this purpose one may add a small amount of a salt as for example a phosphate, of the metal to the fluid time eliminating gum forming constituents, sulfur and the like. The amount of the catalytically active metal or salt which is used may vary from. the fraction of a per cent up to several per cent.

It is to be understoodthat the manipulated steps in the preparation of the catalyst pellets or fragments as well as the form and size thereof are within the knowledge and discretion of those skilled in the art.

We have found that certain advantages are obtained by effecting the reaction within a comparatively narrow range of temperature which depends to some extent on the nature of the gasoline, although it is possible to gain many of the advantages of our invention over a comparatively wide range of temperature. In general, the temperature should be sufficiently high with respect to the time and conditions of contact between the vapor and the scrubbing medium, to convert the gum forming constituents into a physically separable form and preferably without inducing substantial condensation of the gasoline vapors.

When proceeding according to Example II we have found it necessary in redistilling the del canted condensate to reflux or dephlegmate the vapors only slightly, if at all, in order to obtain a good and complete separation of the gum forming polymer from the desired refined gasoline vapors. In general, this separation is not difficult and only a very small amount of fractionation or dephlegmation is necessary to give a very clean separation.

The manner of contacting or scrubbing the vapors of the gasoline with the scrubbing fluid or catalyst pellets is not critical.

In general, any known equipment for effecting contact between a vapor and a liquid, may be used. A very con- 'venient procedure consists in bubbling the vapors through a pool of the catalyst, whichmay consist of a mixture of the acid and some condensed immiscible polymer. Another method of effecting the scrubbing operation consists in spraying the liquid catalytic composition through a tower in countercurrent or parallel direction with respect to the gasoline vapors being treated. If desired, such tower may be filled with a packing, over which the liquid flows downwardly and is then recirculated.

In an analogous manner when a solid catalyst is employed the vapors are contacted with the catalyst by using well knownexpedients for effecting eflicient contact between vapors and solids. I

To remove polymer from the liquid acid scrubbing medium, the scrubbing medium is withdrawn continuously or periodically, permitted to stratify, whereby polymer. rises to the surface and the acid settles to the bottom, after which the acid is returned to the system and the polymer is subjected to recracking or used for other purposes, preferably after washing with water to remove water soluble constituents.

The gasoline condensate obtained after sombbing medium usually contains a small amount of dissolved hydrogen sulfide, which is probably present in the original raw gasoline. This is re.- moved conveniently by contacting the vapors with lime, or washing the condensed gasoline with a small amount of water or an aqueous aikaline solution of soda ash or alkali. This treatment to remove hydrogen sulfide does not in any way change the motor fuel value of the condensate, but serves the function of reducing the odor and corrosion tendency of the gasoline product. After the alkali wash a water white gasoline is obtained which has all of the properties described heretofore.

By using slightly higher temperatures or increasing the amount of steam or both, no polymer separates on the solid catalyst.

In this sepcification we referred to the undesirable constituents of the gasoline, which are separated by our process, asfgum forming constituents, and in the catalyz'ed form these constituents have been referred to sometimes as polymers". Whilewe believe that the material separated, is in fact the gum producing fraction of the raw gasoline in the form of a polymer that includes sulfur impurities'of the raw gasoline,

' the effects.

' gasoline boiling range.

probably in the form of a reaction product of,

some sort or other, it is to be understoodthat our invention is not limited by any theory to explain Similarly, while we refer to the process as a catalytic process (in view of the fact that there appears to be no perceptible consumption in the acid reacting phosphorus reagent), it is to be understood that we are not in a position at this time to classify the nature of the reactions which contribute to the success of our process.

Under the preferred conditions of operation the Engler distillation characteristics of the raw gasoline are not changed substantially. Nevertheless, in view of the relatively wide range of temperature condition which can be used without departing from the scope of our invention, as well as the fact that chemical changes additional to those incident to gum removal may take place, especially as the reaction temperature approaches cracking temperatures, we do not limit ourselves to a product whose'Engler distilling characteristics are exactly reproduced in the final product.

In general, we prefer to operate-below cracking temperatures, that is, temperatures such as are commonly used in the art today in converting relatively high boiling hydrocarbons to those of One of the distinct advantages of our process resides in the fact that widely varying raw cracked gasoline distillates may be treated without necessitating extensive changes in the treating conditions, such as temperature, time of contact, etc. Nevertheless, under some conditions successive treatments such as might be hatl by subjecting the gasoline to two catalytic operations in series or by recycling the stock in a batch-wise'manner, fall within the purview of our invention.

ortho phosphoric acid is probably converted to pyro phosphoric acid and perhaps to meta phosphoric acid. If desired one can add sufficient P205 to retain a on thereof in unreacted form. As a rule there is sufiicient water in the gasoline to combine with such P205 especially after a long" period of treatment, even though the amount of water dissolved in a decanted raw gasoline is very small. One of the advantages of the present invention resides in the fact that the reacted P205 product is itself an excellent catalyst for the purpose of our invention.

Although we have described the principles of 1 our invention and have set forth specific embodiments of the application thereof, it is to be understood that these are illustrative only and that the invention is not restricted to the temperatures, concentrations, rates of flow, etc., specifically set forth. Further, it is to be understood that our process may be operated continuously or otherwise, and at sub-atmospheric pressure as well as superatmospheric pressure, if so desired.

What we claim is:

1. In the catalytic refining of hydrocarbon vapors of gasoline motor fuel boiling range by contact with a catalyst comprising an acid reacting compound of phosphorus below cracking temperature in the presence of water vapor to convert gum forming constituents of the said hydrocarbon vapor to relatively high boiling products as compared to the gasoline being treated and separating the desired gasoline product from the converted gum forming constituents, the steps that comprise removing water from the treated hydrocarbon material as discharged from the catalyst and subsequently separating gasoline from converted gum forming constituents by fractionation.

2. In the catalytic refining of hydrocarbon vapors of gasoline motor fuel boiling range by contact with a catalyst comprising an acid reacting compound of phosphorus below cracking temperature in the presence of water vapor to convert gum forming constituents of the said hydrocarbon vapor to relatively high boiling products as compared to the gasoline being treated and separating the desired gasoline product from the converted gum forming constituents, the steps that 'comprise passing the said vapors as discharged from the catalyst in contact with a substance arating asoline from converted gum forming constituents by fractional condensation.

3. In the catalytic refining of hydrocarbon vapors of gasoline motor, fuel boiling range by contact with a catalyst comprising an acid reacting compound of phosphorus below cracking temperature in the presence of water vapor to convert gum forming constituents of the said hydrocarbon vapor to relatively high boiling products as compared'to the gasoline being treated and separating the desired gasoline product from the converted gum forming constituents, the steps that comprise condensing the said vapors as discharged from. the catalyst, decanting gasoline containing converted gum forming constituents from water, and separating the gasoline from converted gum forming constituents by fractional distillation. I

WALDO C. AULT. CARROLL A. HQCHWALT.

CERTIFICATE OF CORRECTI ON Patent No. 2,131,879. October 1;, 1958.

wALDo c'. AULT., ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent'reqliiring correction as follows: Page 5, second column, line 68, for the word "soil" read solid; page 5, first column, line 19, for "sepcification" read specification; and that the" said'Letters Patent should be read withthis correction therein that the same may conform to the record of the case in the Patent Office. I I

Signed and sealed this 15th day of November, A.- D. 1938.

Henry Van Arsd'ale (Seal) Acting Commissionerof Patents.