US2781296A - Treatment of cracked hydrocarbon distillates with a phenylene diamine, oxygen, and alkali - Google Patents

Description

United States Patent TREATMENT OF CRACKED HYDROCARBON DIS- TILLATES WITH A PHENYLENE DIAMINE, OXYGEN, AND ALKALI Kenneth M. Brown, Hinsdale, 111., and Charles R. McMahan, Houston, Tex., assiguors to Universal ()il Products Company, Des Plaines, 111., a corporation of Delaware No Drawing. Application December 29, 1953, Serial No. 401,074

7 Claims. (Cl. 19629) This invention relates to the treatment of cracked hydrocarbon distillates and more particularly to a novel process for effecting both sweetening of sour hydrocarbon distillates and reduction in the gum content thereof.

One method of treating cracked gasoline containing ever, it has been found that, with some gasolines, this I method of treatment results in the desired sweetening but also results in an excessive increase in the gum content of the gasoline. It now has been found that this increase in gum content is due to the caustic solution utilized during the inhibitor sweetening. The present invention offers a novel method for retaining the improved benefits of inhibitor sweetening and at the same time obtaining reduced gum formation.

In one embodiment the present invention relates to a process for producing a substantially sweet hydrocarbon distillate of reduced gum formation which comprises treating said distillate with caustic solution to remove a major portion of the components which promote gum formation during subsequent sweetening, separating treated distillate from caustic solution, commingling a phenylene diamine inhibitor with the separated distillate, and effecting sweetening thereof in the presence of an oxidizing agent and caustic solution substantially free from impurities promoting gum formation.

In a specific embodiment the present invention relates to a process for producing a substantially sweet cracked gasoline of reduced gum formation, which comprises treating said gasoline with caustic solution to remove a major portion of acidic components from said gasoline, separating treated gasoline from caustic solution, commingling a phenylene diamine inhibitor with the separated gasoline, effecting sweetening thereof in the presence of air and caustic solution substantially free from impurities promoting gum formation, discontinuing the treatment of gasoline when the first mentioned caustic solution becomes saturated with said impurities, withdrawing the thus spent caustic solution and replacing it with the second mentioned caustic solution, and utilizing fresh caustic solution as the second mentioned caustic solution.

The present invention is particularly applicable to the treatment of sour cracked gasoline, including thermally cracked gasoline, catalytically cracked gasoline, reformed gasoline, polyform gasoline, etc., but also may be utilized, with suitable modifications, for the treatment of other gasolines, including substantially saturated gasoline as, for example, straight run gasoline, natural gasoline, etc., when suitably commingled with olefinic or other unsaturated components, and cracked or mixtures of cracked and straight run higher boiling distillates including kerosene, diesel fuel, gas oil, etc.

It will be noted that a hydrocarbon distillate and particularly cracked gasoline is treated with caustic solution to remove a major proportion of the components which promote gum formation during subsequent sweetening. In many uses other acidic components are also removed in this step. The caustic solution generally is utilized as an aqueous solution and may range from about 5 to about 50 Baum gravity. When the hydrocarbon distillate contains hydrogen sulfide, it preferably is given a pretreatment with caustic solution or otherwise to remove the hydrogen sulfide prior to the treatment to remove mercaptans. These caustic treatments may be batch or continuous type of operations and generally are effected at substantially atmospheric temperature, although subatmospheric or elevated temperature which usually will not be above about 200 F. may be employed.

In accordance with the present invention, the caustic solutionutilized for removing the impurities promoting gum formation should be replaced when these impurities appear in the hydrocarbon distillate efiluent from this treating step. It is essential that the final sweetening step be effected in the substantial absence of such impuritiesand, therefore, the impurities should not be included in the hydrocarbon fraction being subjected to the inhibitor sweetening. The use of fresh caustic solution in the inhibitor sweetening step and the proper replacement of the caustic solution in the first treating step generally will result in a final sweetened distillate of reduced gum formation. In some cases, it may be desirable to water wash the distillate from the first caustic treatment in order to insure removal of caustic containing the impurities from the distillate before commingling the inhibitor with the hydrocarbon distillate. In place of water washing, any other suitable treatment to accomplish this may be utilized.

In one embodiment of the invention, when the caustic solution in the first treating step is to be withdrawn, it may be removed from the system and replaced with caustic solution used in the inhibitor sweetening step of the process. Fresh caustic then is utilized in the latter step, and the cycle is repeated as required.

After treatment to remove a substantial proportion of the impurities, the hydrocarbon distillate still will contain a minor proportion of mercaptans, with the result that the distillate is not sweet to the Doctor Test. In accordance with the present invention, a phenylene diamine compound is added to the hydrocarbon distillate, and

. carbon atoms per group, including such compounds as N,N-di-iso-propyl-p-phenylene diamine, N,N'-di-amyl-pphenylene diamine, N,N'-di-hexyl-p-phenylene diamine, etc. It is understood that the alkyl groups may comprise different radicals as, for example, in such compounds as p-phenylene diamine, N-hexyl-N'-octyl-p-phenylene diamine, etc., and that a mixture of the di-alkyl phenylene diamine compounds may be employed. The phenylene diamine compound may be utilized in a concentration of I from about 0.0001% to about 1% by weight and pref- 3 erably of from about 0.001% to about 0.1% by weight of the hydrocarbon distillate.

Because the inhibitor sweetening reaction comprises the converting of mercaptans to disulfides, presumably through an oxidation reaction, it is essential that air be present in the reaction. Generally sufficient air will be dissolved or entrained in the hydrocarbon distillate in order to satisfy this requirement. However, in other cases sufficient air may not be dissolved in the hydrocarbon distillate, particularly when the hydrocarbon distillate is withdrawn from storage tanks having floating roofs, and in such cases air from an extraneous source must be added to the hydrocarbon distillate. It 'is understood that oxygen or other oxygen-containing gases may be used in place of air. i

The hydrocarbon distillate containing the phenylene diamine compound is allowed to remain in contact with air and caustic solution until the distillate becomes substantially sweet. As hereinbefore set forth, the caustic solution used in the sweetening reaction must be substantially free from impurities promoting gum formation. It has now been found and will be shown in the following examples that the use of caustic solution containing such impurities resulted in sweet gasoline but of excessive gum formation. It generally is necessary to utilize fresh caustic in this step of the process. As hereinbefore set forth, one embodiment of the invention comprises utilizing this caustic to replace the caustic solution used in the first step of the process when the latter is to be removed. When desired other materials which facilitate the inhibitor sweetening reaction may be supplied to this step of the process, provided they do not promote gum formation.

The impurities which promote gum formation have not been definitely established but are believed to include thiophenols, secondary and tertiary mercaptans, etc. Regardless of what these impurities actually are, the use of v gasoline is evaporated in approximately 3 hours by means fresh caustic solution in the sweetening step and the proper replacement of the caustic solution in the first step of the process will avoid the difficulties of excessive gum formation in the treated gasoline.

The sweetening reaction may be effected at' substantially atmospheric temperature, which may range from about 50 to about 100 F., or it may be effected at higher temperatures which generally will not be above about 200 F. Usually the sweetening reaction will be efiected within 24 hours although, in some cases, a longer time. may be required.

The sweetening reaction may be effected in a batch type operation, in which the hydrocarbon distillate, air andphenylene diamine compound are allowed to remain in contact with each other for the desired time, generally some means; of mixing being employed including, for example, stirring-blades, recirculation of the mixture, etc; In another; embodiment; the hydrocarbon fraction may be; continuouslyintroduced into the sweetening zone and the distillatecontinuously withdrawn therefrom, the flowrate being regulated. to allow sufficient time of contact in this. zone. Here again means for effecting intimate mixing-may be provided. It isunderstood that the final sweetening- Zone may comprise a conventional storagetank wherein, after sufficient mixing, the caustic is allowed to settle to the bottom of the tank and thereby is separated from the gasoline. In another" embodiment, intimate mixingzrnay be obtained by orifice mixers, etc. prior to introduction intothe sweeteningxzone'. In some cases, it may be desired to water wash the gasoline after' sweetening.

The following examples are introduced to illustrate further the novelty and utility of the present invention but not. with the intention of unduly limiting the same.

Thegum content of thev gasoline was determined. by the copper dish method which, is a standard method of" determining gum, in gasoline. According to this method,

100. ml. of gasoline. is placed in a copper. dish. and-the:

of a steam bath and a controlled passage of air over the open top of the dish. The weight of residue in the copper dish is reported as mg. of copper dish gum per 100 ml. of gasoline.

Example I The gasoline used in this example was polyform cd gasoline. When treated with 20 Baum caustic solution to reduce the mercaptan content of the gasoline to 0.0198% by weight and then stored with about 0.01% by weight of l-l,N-di-sec-butyl-pphenylene diaminc for 144 hours, the mercaptan content was reduced to 0.006% by weight but the gasoline had a copper dish gum content of 42 mg. per 100 ml. of gasoline.

Example 1! Another sample of the same gasoline was stored in the same manner as described above but the caustic solution used in the inhibitor sweetening step was a fresh solution of 20 Baum caustic. After 12 hours in storage, the gasoline was sweet and had a copper dish gum content of only 6 mg. per 100 ml. of gasoline. It wiil be noted that the use of fresh caustic in the inhibitor sweetening step produced both a sweet gasoline and a gasoline of low gum content.

Example III Another sample of the gasoline was treated in the manner hereinbefore set forth, but the caustic used in the inhibitor sweetening step contained 4% acid oils. This caustic previously had been used for 24 hours to treat the gasoline to remove acidic components. After 48 hours in storage, this gasoline was sweet but had a copper dish gum content of 62 mg. per 100 ml. of gasoline.

We claim as our invention:

1'. A process for producing a substantially sweet hydrocarbon distillate of reduced gum formation which comprises treating sour distillate with caustic solution to remove a major portion of components which promote gum formation during subsequent sweetening, separating treated distillate from caustic solution, commingling a phenylene diamine inhibitor with the separated distillate and effecting sweetening thereof in the presence of an oxidizing agent and fresh caustic solution substantially freefrom impurities promoting gum formation.

2. A process for producing a substantially sweet cracked hydrocarbon distillate of reduced gum formation which comprises treating sour crackeddistillate with caustic solution, to remove a major portion of components which promote. gum formation during subsequent sweetening, separatingv treated distillate from caustic solution, can mingling a. phenylene diamineinhibitor with the separated distillate and effecting. sweetening thereof in the presence of 'air and: fresh. caustic solution.

3.. The process of claim 2 further characterizedin that; said: sour distillate is cracked gasoline.

4'. The process of claim 1 further characterized in that'said sou-r distillate is poly-formed gasoline;

5:. The process of claim 2 further characterized in that said phenylene'diam'ine inhibitor is' N,N-"-di sec-'butylp-phenylene diam-tine. p

6; A; process for producing a substantially sweet hydrocarbon distillate of reduced gum formation, which comprises treating sour distillate with caustic solutionto remove a major portion of' componentswhich promote gum formation during subsequent sweetening, separating treated distillate from caustic solution, :commingling' a phenylene diami-ne inhibitor with theseparated distillate, effectingisweetening thereof in 'the presence of an oxidizing. agent and caustic solution substantially free from impurities promoting gum formation, discontinuing. the treatment of the distillate when-the first'mentionedcaustic' solution: becomes saturated with said" impurities, with? drawing-:the' spentcaustic solution a'nd repl'ac'ing' it with gasoline When the first mentioned caustic solution becomes saturated with said impurities, withdrawing the spent caustic solution and replacing it with the second mentioned caustic solution, and utilizing fresh caustic solution 5 as the second mentioned caustic solution.

References Cited in the file of this patent UNITED STATES PATENTS Browder May 8, 1951 2,616,833 Chenicek et al. Nov. 4, 1952

Claims (1)

1. A PROCESS FOR PRODUCING A SUBSTANTIALLY SWEET HYDROCARBON DISTILLATE OF REDUCED GUM FORMATION WHICH COMPRISES TREATING SOUR DISTILLATE WITH CAUSTIC SOLUTION TO REMOVE A MAJOR PROTION OF COMPONENTS WHICH PROMOTE GUM FORMATION DURING SUBSEQUENT SWEETENING, SEPARATING TREATED DISTILLATE FROM CAUSTIC SOLUTION, COMMINGLING A PHENYLENE DIAMINE INHIBITOR WITH THE SEPARATED DISTILLATE AND EFFECTING SWEETENING THEREOF IN THE PRESENCE OF AN OXIDIZING AGENT AND FRESH CAUSTIC SOLUTION SUBSTANTIALLY FREE FROM IMPURITIES PROMOTING GUM FORMATION.