US2192174A - Vapor phase refining of hydrocarbon distillates - Google Patents

Description

Patented Mar. 5, 1940 UNITED STATES PATENT OFFICE VAPOR PHASE REFINING F HYDROCARBON DISTILLATES ware No Drawing. Application March 3, 1936, Serial No. 66,894

4 Claims.

This invention relates to the refining of petroleum distillates for motor fuel purposes which are rich in impurities that impart color and odor, or are productive of gum. In addition, the invention 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 malodorous, off color, rich in gum forming constituents, 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 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 olefinic 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 a compromise between gum and sulfur 5 impurities on the one hand and cost of refining reagents and sacrifice in yield on the other. Thus, for example, a treatment with sulfuric acid may lower the antiknock value of a fuel 5 to points if a substantially gum free and low 10 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 5 has no efiect 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 in- 90 hibitors 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 disulfides. This is usually accomplished with the aid of a source of oxygen. The presence of small quantities 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 disulfldes, impairs color stability and promotes corrosion. The effect 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 Journal 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 constituents.

(,5) Substantial reduction of sulfur impurities.

(6) Improved susceptibility to, and permanence of tetra ethyl lead treatment.

(7) Improved color stability.

(8) Nearly total elimination of treating reagent and processing operation costs.

(9) Recovery of gum and sulfur components in a non-corrosive utilizable form. I (10) General appplicability of refining method to widely varying raw gasolines. whereby a product having a high induction period is readily and conveniently obtained.

In a co-pending application which we have filed of even date we disclosed a process for refining raw gasoline characterized in that raw gasoline vapors are scrubbed with a solid or a mobile liquid catalytically active scrubbing medium, such for example, as phosphoric acid. The temperature conditions, time and condition of contact between the scrubbing medium and the gasoline vapors, as well as the. concentration and activity of the catalyst present in the scrubbing medium, are preferably so adjusted with respect to each other as to convert substantially all of the gum forming impurities and a considerable portion of procedure, we have shown that raw gasoline while in liquid phase may be heated in admixture with the catalysts of our invention, whereby the impurities are converted into the relatively high boiling form. Subsequently the gasoline so treated is separated from the acid catalyst as by decantation, the catalyst is returned for reuse and the decanted gasoline product distilled to remove the high boiling polymers constituting the objectionable impurities.

As a further modification of our invention we have shown that when raw gasoline vapor containing steam is subjected to the action of our catalysts the polymerizing effect is not necessarily impeded by the steam, but separation of the poly mers is not attainable by a simple fractional condensation. In such case it is desirable to condense the vapors, separate the water layer by decantation and subsequently redistill the substantially water-free product whereby the polymer is recovered as a high boiling end; Alternatively, the vapor mixture of treated gasoline, steam and polymerized impurities may be treated in vapor phase to remove the water, as for example, by contacting such vapors with lime (CaO) whereupon the high boiling polymers can be separated from the vapors by fractional condensation or rough fractional distillation. As a further alternative, the foregoing vapor mixture may be conducted through a scrubbing fiuid or known solids having adsorbtive properties whereby the polymer is scrubbed from the vapor mix- 1 ture. A large variety of scrubbing fluids will be found efiective for this purpose, including phosphoric acid, paramn, lubricating oils of sufflcient- 1y high boiling point as to be substantially nonvolatile under the conditions of the scrubbin operation.

The present invention represents a modified form of the foregoing procedures described in our co-pending applications. It consists in the use of substantially water-free raw gasoline vapors and catalysts of the same general class as we have described in our aforementionedv applications and is distinguished by the fact that the temperature conditions during the catalytic polymerizing treatment are maintained at a sufflciently high level to prevent substantial condensation of the polymers formed during the catalysis. The vapor mixture so obtained is then condensed and redistilled to remove the high boiling polymer as a high boiling end or preferably, the vapor mixture is fractionally condensed whereupon the high boiling polymer is thrown out and thereby separated from the desired gasoline vapor product. This desired gasoline vapor product is then con;- densed and collected in a separate receiver and is ready for marketing except perhaps for a mild aqueous alkaline wash to remove hydrogen sulfide.

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

Original Treated Gum value ..cu. dish.. 575 v 4 Sulfur content percent" l8 .0 Bromine unsaturatio umber. 61 59 67 68 Yellow Water white pcrcent. 98

Weare 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. 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 (U. S. Patent 1,709,315). However, such process is ineffective or only partially effective at best and must be supplemented by additional chemical treatments, such as, for example, a hypochlorite treatment. Furthermore, the various acids of phosphorus have been considered ineffective in and of themselves for the purpose of refining raw gasoline (U. S. Patent 1,914,955), and to the best of our knowledge theuse of these acids has met with no commercial success in this field.

In contrast with the foregoing, the following examples illustrate specific procedures for ap plying the principles of our invention:

Example I 230 to 240 C. by an oil bath that surrounded all except a small portion of the upper extremity of the catalyst containing vessel. Some of the polymer formed was retained in the catalyst mixture. However, much of the polymer was carried over with the gasoline vapors inasmuch as the condensate showedhigh gum content. By

redistilling the condensate using only a rough fractionation a product of excellent motor fuel quality was obtained, the polymer being recovered as a high boiling end.

From time to time a portion of the catalyst mixture was withdrawn and replaced with an equivalent amount of substantially water free phosphoric acid. The mixture so withdrawn was allowed to stratify whereupon the polymer rose to the surface of the acid layer and was separated by decantation. The acid layer was then ready to be returned to the catalyst containing vessel.

The gasoline was of perceptibly improved antiknock quality, contained only a negligible amount of gum, and had a sulfur content considerably below that of the starting material.

Example II Proceed as in Example I, insofar as the catalyst is concerned, but instead of condensing the vapors completely, subject them to a dephlegmation or fractional condensation in which approximately two to four per cent of the total vapor mixture is condensed. In this manner the high boiling polymers are separated without resorting to a total condensation and redistillation.

While the foregoing procedure is preferred it is to be understood that other means for removing the undesirable high boiling fraction of the vapor mixture may be employed, thus, for ex ample, a selective scrubbing step in which the vapors are scrubbed with a substantially nonvolatile liquid having an afiinity or solvent action, or otherwise capable of holding back the high boiling end may be employed. Suitable materials for this purpose include the high boiling hydrocarbon'oils, paraffins,'etc. which are substantially non-volatile under the conditions of the scrubbing operation.

Example III Substitute for the acid in Example I 85% phosphoric acid of commerce and otherwise proceed as in Examples I or II. The first portion of the run will be found to produce a cloudy condensate which contains an appreciable amount of water. As the treatment proceeds the acid concentration attains equilibrium conditions with respect to water content after which the subsequent condensate is recovered in a separate receiver and redistilled as in Example I, to separate the gum.

Instead of condensing the vapors and redistilling the condensate to separate the polymer, the vapors may be fractionally condensed or otherwise treated as in Example II.

Example IV Substitute for the catalyst of Example III aqueous thiophosphoric acid and otherwise proceed as in Example III.

Example V To illustrate the application of the principles of our invention to a process in which the gasoline is in a vapor state, and the catalyst is solid or is deposited on a solid carrier of fragmentary or pellet form rather than the fluid or suspended mobile form, as in the case of the preceding examples, the gasoline vapor mixture as described in Ex ample I 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 maintained at 225 to 240 C. to prevent substantial condensation of the polymer. Even under these conditions some polymer was formed, but it was found to be fluid and soon collected at the bottom of the tube. The tower consisted of a two inch glass tube thirty inches long, lagged and electrically heated to maintain the desired temperature conditions.

In lieu of the pumice granules there were substituted granular pellets of clay made by mixing clay with approximately 25 per cent by weight of per cent phosphoric acid and suflicient water to produce a moldable mix. The mix was formed into pellets and dried at C., after which it was packed 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 carbon or other adsorbent 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 solid carrier for the active component.

Example VI Add to the phosphoric acid of Example I approximately one per cent of a mixture of equal parts by weight of copper and cadmium hydroxides and otherwise proceed as in Example I. The final product will be found to have the desired motor fuel characteristics insofar as gum and sulfur are concerned, as well as antiknock quality.

Example VII A commercial cracked gasoline was treated in an all metal unit by feeding the vapors at the temperature as set forth in Example I through four one-eighth inch orifices through an 8 inch depth of H3PO4 catalyst maintained at 235-240 C. The vapors were treated at a rate equal to 2,000-2,500 c. c. of raw gasoline liquid per hour; after passing through the catalyst, the vapors were introduced into a small dephlegmator or fractionating tower partly filled with packing for the purpose of removing the last traces of entrained and vaporized polymer. The reflux ratio to be effective for this purpose need be very small. From the top of the fractionating device the vapors were led to a condenser.

After a mild aqueous alkaline wash for hydrogen sulfide removal the condensed gasoline was found to have the following characteristics, which by comparison with those of the original material further demonstrate the value of our process:

Original Treated Gum value... 180 2 Sulfur content percent 0. l6 0. 1o Octane value... 66 69 Color Yellow Water white Oxygen bomb stability. l. 5 75 materials of construction, such as carbon et a1.

' It is to be understood that the temperature of f the temperature of the entering gasoline vapors.

According to one embodiment the catalyst is preferably a liquid under the conditions of the treatment and is preferably substantially insoluble in the polymer that is formed and with part of which polymer it may be in intimate mixture while in use. Inasmuch as the catalyst is immiscible, it separates from the polymer upon standing and may be recovered as by decantation and returned to the process. In this way the catalyst may be used indefinitely as there is no perceptible loss except that attributable to usual mechanical losses incident to the handling of any material.

While ortho phosphoric acid is admirably suited for the purpose of our process, in thatit not only efiects substantially complete conversion of the gum forming constituents into separable form, but in addition attains the other 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 IbPSOa, 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 85 per cent H3P04. However, if desired, one may use 100 per cent H3PO4 by adding suflicient 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 I-IaPO4, 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 P205 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.

While we prefer to use a catalytic composition which is immiscible with the polymer, whereby it may be separated from the accumulated polymer by stratification 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.

A further modification of the catalytic composition consists in the use of catalytically active salts either 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 acid catalyst or one may incorporate a small amount of oxide directly to the acid, in which case the oxide probably combines with the acid to form the salt in situ. The efiect of the addition of the salts is to reduce the temperature of the reaction or the required time of contact, and

to some extent in changing the nature of the hydrocarbons being treated as to improve substantially the antiknock value, while at the same time eliminating gum forming constituents, sulfur and the like. The amount of the catalytically active metal or salt which is used may vary from a fraction of a per cent up to several per cent.

It is to be understood that 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.

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.

convenient procedure consists in bubbling the vapors through a pool of the catalyst, which may 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 known expedients for effecting eflicient contacts between vapors and solids.

a large part of the polymer formed under the temperature conditions described therein, is carried through the treating tower without condensation. By reducing the temperature, it is possible to condense the polymer, as formed, as a mobile fluid without substantial condensation of the treated gasoline vapors which may be condensed and recovered in a separate receiver, preferably after a rough fractional distillation to remove traces of polymer vapors and entrainment. The fact that the polymer is mobile and drains freely from the solid catalyst at the temperature of the treatment, avoids fouling of the catalyst. However, from time to time one may inject super-heated steam into the treating tower whereby any deposits of polymer are effectively removed. The polymer which collects at the bottom of the tower may be recracked if desired, particularly if the amount of sulphur in the raw gasoline is not excessive, and the polymer thereby obtained is correspondingly low in this impurity.

In this specification we referred to the undesirable constituents of the gasoline which are separated by our process, as gum forming constituents; and in the catalyzed form these constituents have been referred to sometimes as polymers. While we believe that the material separated is in fact the gum producing fraction of the raw gasoline in the form of a polymer .that includes sulphur impurities of the raw gasoline, probably in the form of a reaction product of some sort or other, it is to be understood that our invention is not limited by any theory to explain the effects. Similar y, while we refer to th 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 gasoline boiling range. 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 had 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.

We have found it convenient in preparing the catalyst to dissolve or suspend P205 in phosphoric acid of commerce which acid usually contains about 15% water. By adding suflicient P205 the ortho phosphoric acid is probably converted to pyro phosphoric acid and perhaps to meta phosphoric acid. If desired, one can add suflicient P205 to retain a portion thereof in unreacted form. As a rule there is suflicient 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 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, 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 super-atmospheric pressure, if so desired.

What we claim is: I

1. The process of treating a hydrocarbon fraction of gasoline motor fuel boiling range containing gum forming constituents having boiling points within the said boiling range to convert said gum forming constituents to bodies of higher boiling range and removing the converted gum; forming constituents comprising passing vapor of the said hydrocarbons substantially free of steam in contact with a catalyst body substantially free of sulfuric acid and comprising an acid of phosphorus at a temperature sufficiently high to prevent substantial condensation of the converted gum forming constituents and subsequently. separating converted gum forming constitutents from the treated hydrocarbon fraction, whereby said gum forming constituents are converted to products boiling substantially above the boiling range of the hydrocarbon fraction being treated and are readily removed from the said fraction by physical means in the absence of water vapor and the said fraction is thereby rendered substantially free of gum forming constituents while contamination of the catalyst is avoided to a large extent.

2. The process of treating a hydrocarbon fraction of gasoline motor fuel boiling range containing gum forming constituents having boiling points within the said boiling range to convert said gum forming constituents to bodies of higher boiling range and removing the converted gum forming constituents comprising passing vapor of the said hydrocarbons substantially free of steam in contact with a catalyst body substantially free of sulfuric acid and comprising an acid of phosphorus at a .temperature sufliciently high to prevent substantial condensation of the converted "gum forming constituents and subsequently separating convertedgum forming constituents from the treated hydrocarbon fraction by fractional condensation, whereby said gum forming constituents are converted to products boiling substantially above the boiling range of the hydrocarbon fraction being treated and are readily removed from the said fraction by fractional condensation in the absence of water vapor and the said fraction is thereby rendered substantially free of gum forming constituents while contamination of the catalyst is avoided to a large extent.

3. The process of treating a cracked hydrocarbon fraction of gasoline motor fuel boiling range containing gum forming constituents having boiling points within the said boiling range to convert said gum forming constituents to bodies of higher boiling range and removing the converted gum forming constituents comprising passing vapor of the said hydrocarbons substantially free of steam in contact with a catalyst body substantially free of sulfuric acid and comprising an acid of phosphorus at a temperature sufliciently high to prevent substantial condensation of the converted gum forming constituents and subsequently separating converted gum forming constituents from the treated hydrocarbon fraction by scrubbing the vapors at a tem-- perature sufiiciently high to avoid substantial condensation of the said hydrocarbon fraction with a liquid having selective aflinity'for the converted gum forming constituents and subsequently condensing the scrubbed vapor, whereby said gum forming constituents are converted to products boiling substantially above the boiling range of the hydrocarbon fraction being treated and are readily removed from the said fraction I by said scrubbing in the absence of water vapor and thesaid fraction is thereby, rendered substantially free of gum forming constituents while contamination of the large extent.

' avoided to a large extent.

catalyst is avoided to a 4. The process of treating a cracked hydrocarbon fraction of gasoline motor fuel boiling range containing gum forming constituents having boiling points within the said boiling range to convert said gum forming constituents to bodies of higher boiling range and-removing the converted gum forming constituents comprising passing vapor of the said hydrocarbons substantially free of steam in contact with a catalyst body substantially free of sulfuric acid and comprising phosphoric acid at a temperature sufliciently high to prevent substantial condensationof the converted gum forming constituents and subsequently separating converted gum forming constituents from the treated hydrocarbon frac tion, whereby said gum forming constituents are converted to products boiling substantially above the boiling range of the hydrocarbon fraction. f,

being treated and are readily removed-'frornvthe said fraction by physical means in-.the,.absence of water vapor and the said fraction is thereby rendered substantially free of gum forming con l the catalyst is stituents while contamination of WALDO c. AULT. t

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