US2953522A - Treatment of catalytically cracked distillates with polyalkylphenol prior to alkali treatment - Google Patents

Description

. Patented SepLZO, 1960.

T me S te Pmn fiice.

i 2,953,522 i TREATMENT OF CATALYTICALLY CRACKED DISTHJLATES W I T H POLYALKYLPHENOL PRIGR TO ALKALI TREATMENT Willem J. Wolfson, The Hague, Netherlands, assignor to Shell Oil Company, New

Delaware j V v H 7 No Drawing. Filed June 25,1956, Ser. No. 593,360 Claims priority, application Netherlands June 30, 1955 8 Claims. (Cl. 208-231) This invention relates to a process for the preparation of hydrocarbon fractions of improved oxidation stability, particularly distillates obtained in the catalytic cracking of petroleum.

In the catalytic cracking of petroleum oils distillate fractions are produced which contain characteristically high concentrations of aryl mercaptans produced in the cracking process and relatively small concentrations of alkyl mercaptans, the form in which most of the mercaptan sulfur occurs in straight run, thermally cracked and thermally reformed distillates. Such aryl mercaptans, in which an SH group is attached directly to a benzene ring, include thiophenol, thiocresols and thioxylenols. The presence of these compounds, together with the olefins and diolefins which always occur in high concentrations in catalytically cracked distillates, results in 'a serious refining problern. Upon contact with air, even in extremely small amounts, the distillate rapidly deteriorates because of the accelerating effect of the aryl mercaptans or (aryl disulfides into which they are converted) in the oxidation of olefins and'diolefins. Intolerable amounts of peroxides and gum result, and oxidation products are formed which, especially in the case of. gasoline, are precursors of engine induction system deposits;

Heretofore, it has been thepractice to avoid this oxidative deterioration of catalytically cracked distillates by York, N.'Y., a corporation of found that it is not necessary to bring the crude cracked products immediately into contact with alkali metal hy droxide solution. It has been found that the above objects are accomplished when one or more'particular polyalkylphenols are added to the crude cracked products before they are brought into contact with the alkali metal hydroxide solution and before they come into contact with free oxygen.

The crude cracked distillate to which the polyalkylphenol is added accordingto the invention may remain exposed to the air for some time, e.g., 24 hours, without a troublesome amount of compounds being formed which might give rise to the formation of gum. If the crude cracked distillate is then "afterwards washed'with caustic alkali, most of the gum precursors which may have formed areremoved. The presenceof the polyalkylphenol also prevents any'oxygen dissolved in the caustic alkali from-oxidizing the aromatic mercaptans in the caustic alkali phase to disulfides. This is especially advantageous, as the disulfides are not readily soluble in caustic alkali'but dissolve readily in the hydrocarbon I oil,'as a result of which there is a possibility that they removing the aryl mercaptans contained therein by conv tacting the distillates with an aqueous solution of an alkali metal hydroxide, such as sodium hydroxide, before any oxygen in the form of air or otherwise is allowed to come in contact with the distillate. According to the process described in the Strickland patent, US. 2,525,152, El

extreme precautions must also be taken to exclude all air or oxygen during the removal of the aromatic mercaptans and it is recommended that the caustic solution used be freed of oxygen by purging with an inert gas.

Often, however, it is impossible, or at least inconvenient and expensive, to conduct commercial operations with such assiduous attention to the avoidance of any contact between the catalytically cracked distillate and air until after the aryl mercaptans have been entirely ically cracked distillates. Arnore particular object is to 3 provide such a process wherein the qualityof the treated product is improved with respect to; oxidation stability, and content of gum, peroxides and other oxidation products. An important object is also to provide suchja process which does not require the; complete avoidance :1. g

of contact of the cracked distillate withoxygen prior to its treatment with an alkali metal hydroxide solution. Other objects will be apparent in the description of' the invention. ff Contrary to the view hitherto held it has now been will afterwards cause gum formation. are formed the total sulfur content of the cracked distillate is'alsoreduced bythe subsequent contacting with alkali metal hydroxide solution.-

The catalytically cracked distillates to which the present invention is directed are those which are produced from petroleum derived straight run hydrocarbon feed stocks boiling above the gasoline boilingrange, especially those which have relatively high total sulfur concentrations suchas 0.5% by weight or more. Such distillates include gasoline and light and heavy gas oils and have boiling points (ASTM D-86) ranging from about 50 C; to about 410" C. 'Before any contact with air or alkaline solution, these distillates contain total mercaptan sulfur concentrations ranging from about 0.001 to about 0.05 by weight, at least one-tenth (by weight) of which, and often one-half ormore of which isaryl mercaptan sulfur. The influence of the added polyalkylphenol is not sufficient to prevent the. oxidation of hydrogen sulfide.

to free sulfur in the presence of oxygen, so it is preferred that anyhydrogen sulfide present in the total product of the cracking operationberemoved before the cracked distillate comes in contact 'with air. The advantages of the invention a re' most readily obtained when this is done by fractionation, as in the normal distillation of the total cracked product into one or more gas oil fractions, stabilized gasoline, and the lighter-than-gasoline fraction. The hydrogen sulfide inthe total product will be recovered in the latter fraction. The gas oil fractions and the stabilized gasoline are then suitably treated in the process of the invention.

The particular polyalkylphenols which, according to.

the invention, are added to a catalytically cracked distillate before the distillate comes in contact with oxygen are the caustic-insoluble, sterically hindered, ortheo-disubstituted phenols in which at least one and preferably each ortho-substituent isa branched chain alkyl group containing at least 3, and preferably no more than 5 car- 4-dimethyl-6-tert.butylphenol,. 2,6.-di:tert.butylphen0l, 2,

3 6-di-tert.butyl-4-isopropylphenol, 3,3'-dimethyl-4,4'-dihydroxy-5,5-di-tertbutylbiphenyl, 3,3',5,5'-tetraisopropyl- 4,4 dihydroxybiphenyl, bis( 2 hydroxy 3 tert.butyl-5- methylphenyl methane, 2,2-bis 3 ,5'-ditert.butyl4'-hydroxyphenyl)pentane, and the like.

The amount of the polyalkylphenol added is from about 0.001 to about 0.05% by weight of the catalytically cracked distillate. It is preferred, however, that at least about 0.01% by weight be used, and usually no more than 0.025% by weight will be required.

Besides the particular advantage in preventing deterioration of aryl mercaptan-containing cracked distillates upon contact with air, a further reason for selecting the particular polyalkylphenols described is that they are not removed by subsequent treatment of the distillate with aqueous alkaline solutions and they are especially effective inhibitors for the usual purpose of preventing oxidative deterioration of treated (e.g., sweetened or dethiolized) distillates. Therefore, in the practice of the invention, a double addition of inhibitor is unnecessary. Other compounds which are normally used as inhibitors in treated distillates are not only less suitable for the primary purpose of the invention but are often soluble in aqueous alkaline solutions, as are alkylaminophenols and alkylcatechols, which are often used to inhibit oxidative deterioration of treated distillates. The di(alkylamino)benzenes, such as N,N-di-sec.butyl-para-phenylene diamine, while not soluble in aqueous alkaline solutions, are not suitable in the practice of the invention because they do not sufiiciently avoid the formation of peroxides, and in the case of gasoline, give rise to induction system deposits.

While the distillate can be allowed to come in contact with oxygen as soon as the polyalkylphenol has been thoroughly dispersed in the distillate, it is desirable that any such contact not be unduly prolonged. It is pre ferred that the distillate be contacted with an aqueous alkali metal hydroxide solution, for the removal of the aryl mercaptans, within 2 to 3 days, and preferably within 24 hours, after the polyalkylphenol has been added. Sodium hydroxide and potassium hydroxide solutions are preferred, especially the former. Concentrations of such solutions can range from 5 to 50 B. and the amounts used can range from 5% to 50% by volume based on the amount of distillate contacted therewith.

The following example is illustrative of the invention:

EXAMPLE A Kuwait straight run flashed distillate with a boiling range of 300 C. to 550 C. and a total sulfur content of 2.25 to 2.30% by weight was catalytically cracked. The gaseous cracked products, the hydrogen sulfide and the components heavier than gasoline were removed by distillation, after which the following experiments were carried out with the gasoline obtained.

The gasoline was drawn off in an oxygen-free, nitrogen atmosphere and immediately analyzed. In one case 0.020% by weight of 2,6-di-tert.butyl-4-methylphenol, calculated on the hydrocarbon oil, was previously added, while another sample was analyzed without this The peroxide number was determined by the method of Yule and Wilson, Ind. Eng. Chemistry 23, 1254 (1931).

The results of Table I show that even during the analysis the aryl mercaptans were oxidized by atmospheric oxygen, however carefully the analysis was carried out.

The above samples were then exposed to the air for 24 hours before being again analyzed, and the results The results show that a cracked product which has been exposed to the air for 24 hours has obtained a peroxide number and a gum content which are both too high for a readily salable product.

The above samples were then washed with caustic alkali and again analyzed. The results obtained are summarized in Table III. In this case and in the following experiments the caustic alkali washing was carried out with 0.5% by volume of 6 N-sodiurn hydroxide solution (about 26 B.), calculated on the hydrocarbon oil treated.

Table III 2,6-di-tert. butyl-4- Exposed to Air for 24 Hours methylphenol and Then Caustic Washed With Without Percent by weight of aryl mercaptan sulfur content nil nil Percent by weight of alkyl merceptan sulfur content 0.0032 0.0025

Total percent by weight of mercaptan sulfur content 0.0032 0. 0025 Peroxide number, meq. active oxygen per liter of hydrocarbon oil 0. 106 0. 317 Gum (ASTM D-38l) mg./ cc 7 14 The cracked gasoline which was exposed to the air for 24 hours without the polyalkylphenol is found to have too high a gum content, while the peroxide number is so high that it may be assumed that when stored and/or used an even much larger amount of gum will be formed. The gasoline treated with the inhibitor has, however, a reasonable ASTM gum content (10 mg./ 100 cc. is the permissible maximum) and, in addition, the peroxide number is not so high that too much gum formation is to be expected later.

Table IV shows the results of the experiments which were carried out with the cracked gasoline, mentioned in the commencement of the example, to which 0.005% by weight and 0.02% by weight of N,N-di-sec.-butylpara-phenylene diamine (Inhibitor X) had been added, after which the gasoline was exposed to the air for 24 hours. At the same time an analysis is given of these two samples after they had been washed with caustic alkali. A comparison of the data of Table IV with the data of Tables II and HI shows that the inhibiting effect of 2,6-di-tert.-butyl-4-methylphenol is very much better than that of Inhibitor X and that the cracked gasoline 5 inhibited with the latter compound has too high a peroxide number even after a washing with caustic alkali.

Table IV Wghb Wtho 0.005 y 0.02 o y With With wt. of wt. of 0. 005% by 0.02% by Inhibitor X, Inhibitor X,

wt. of wt. of thereafter thereafter Inhibitor X, Inhibitor X, exposed to exposed to thereafter thereafter the air for the air for exposed to exposed to 24 hours, 24 hours, the air for the air for subsequentsubsequent- 24 hours 24 hours 1y washed ly washed with with caustic caustic alkali alkali Percent by weight of aryl mercaptan sulfur content nil 0. 0008 nil nil Percent by weight of alkyl mercaptan sulfur content 0. 0068 0. 0061 0.0019 0.0013

Percent by weight of total mercap tau sulfur content 0. 0068 0. 0069 0.0019 0. 0013 Peroxide number, meq. of active oxygen per liter of hydrocarbon 011-..- 6. 49 6. 33 0. 558 0.651 Gum (ASTM D- 381), mg./100 cc 17 20 5 6 I claim as my invention:

1. A process for preparing a catalytically cracked distillate of improved oxidation stability which comprises adding to a catalytically cracked distillate containing aryl mercaptans and olefinic materials from about 0.001 to about 0.05% by weight of a caustic-insoluble polyalkylphenol before the distillate is allowed to come in contact with oxygen, thereafter contacting the distillate with an aqueous alkali metal hydroxide solution without the need of excluding air, said contacting being achieved without the occurrence of significant oxidative deterioration of the distillate and recovering a distillate of improved oxidation stability and having a reduced sulfur content.

2. A process for preparing a catalytically cracked distillate of improved oxidation stability which comprises distilling a total catalytically cracked product, before it is allowed to come in contact with oxygen, to recover a distillate boiling above about 50 C. and containing from about 0.001 to about 0.05 by weight mercaptan sulfur, at least one-tenth of which is aryl mercaptan sulfur and containing olefinic materials, adding to said distillate,

before the distillate is allowed to come in contact with oxygen, from about 0.001 to about 0.05 by weight of a caustic-insoluble ortho-di-substituted polyalkylphenol containing only carbon, hydrogen and oxygen atoms and from 10 to 40 carbon atoms, at least one of the ortho substituents of which is a branched-chain alkyl group containing at least 3 carbon atoms, contacting the distillate with an aqueous alkali metal hydroxide solution without the need of excluding air, said contacting being achieved without the occurrence of significant oxidative deterioration of the distillate and recovering a distillate of improved oxidation stability and having a reduced sulfur content.

3. A process in'accordance with claim 2, wherein the distillate is a gasoline fraction.

4. A process in accordance with claim 2, wherein the distillate is a gas oil fraction.

5. A process in accordance with claim 2, wherein the polyalkylphenol is a mononuclear phenol each of the ortho substituents of which is a branched-chain alkyl group containing from 3 to 5 carbon atoms.

6. A process in accordance with claim 5, wherein the polyalkylphenol is 2,6-di-tert.-butyl-4-methylphenol and the amount added to the distillate is from about 0.01 to about 0.025% by weight.

7. A process in accordance with claim 2 wherein the polyalkylphenol-containing distillate is contacted with the aqueous alkali metal hydroxide solution in the presence of air.

8. A process in accordance with claim 2 wherein the polyalkylphenol-containing distillate before treatment with the aqueous alkali metal hydroxide solution is exposed to air.

References Cited in the file of this patent UNITED STATES PATENTS 2,346,497 Lovell et al Apr. 11, 1944 2,479,948 Luten et a1 Aug. 23, 1949 2,525,152 Strickland et al Oct. 10, 1950 2,543,953 Backensto Mar.6, 1951 2,552,399 Browder May 8, 1951 2,616,831 Rosenwald Nov. 4, 1952 2,638,412 Browder May 12, 1953 2,645,603 Crammer July 14, 1953 2,721,804 Rosenwald Oct. 25, 1955 2,756,184 Brehm et a1 July 24, 1956 2,772,220 Bushnell et al Nov. 27, 1956 2,843,495 Chenicek July 15, 1958

Claims (1)

1. A PROCESS FOR PREPARING A CATALYTICALLY CRACKED DISTILLATE OF IMPROVED OXIDATION STABILITY WHICH COMPRISES ADDINT TO A CATALYTICALLY CRACKED DISTILLATE CONTAINING ARYL MERCAPTANS AND OLEFINIC MATERIALS FOR ABOUT 0.001 TO ABOUT 0.05% BY WEIGH OF A CAUSTIC-INSOLUBLE POLYALKYLPHENOL BEFORE THE DISTILLATE IS ALLOWED TO COME IN CONTACT WITH OXYGEN, THEREAFTER CONTACTING DISTILLATE WITH AN AQUEOUS ALKALI METAL HYDROXIDE SOLUTION WITHOUT THE NEED OF EXCLUDING AIR, SAID CONTACTING BEING ACHIEVED WITHOUT THE OCCURRENCE OF SIGNIFICANT OXIDATIVE DETERIORATION OF THE DISTILLATE AND RECOVERING A DISTILLATE OF IMPROVED OXIDATION STABILITY AND HAVING A REDUCED SULFUR CONTENT.