US2242624A - Process for stabilization of copper treated oils - Google Patents

Description

Patented May 20, 1941' PROCESS FOR STABILIZATION OF COPPER TREATED OILS Walter A. Schulze, Bartlesville, 0kla., and Graham H.. Short, Phillips, Tex., assignors to Phillips Petroleum Company, a corporation of Delaware No Drawing. Original application November 9, 1938, Serial No. 239,731. Divided and this application May 28, 1940, Serial No. 337,736

2 Claims.

This invention relates to a new and useful process for treating hydrocarbon oil. More specifically, this invention relates to a process for stabilizing or preventing the deterioration of hydrocarbon oil which has undergone a purifymg treatment with reagents containing copper.

This application is a division of our copending application Serial Number 239,731, filed November 9, 1938.

Hydrocarbon oil, particularly petroleum distillates usually contain impurities, including sulfur compounds, whichcause the oil to exhibit undesirable properties such as bad odor and gum and color formation- It is customary, therefore, to subject said impure oil to a purifying treatment in order to remove the impurities or to convert them to less objectionable forms, for example, the conversion of mercaptans to disulfides.

The methods of treatment for the removal or conversion of mercaptans make use of various chemical processes, and of these processes, one of the most satisfactory is the process utilizing copper, salts of copper, or solutions containing copper salts.

\ However, subsequent to. treatment with coppercontaining reagents, it has been found that many hydrocarbon oils require further treatment 01' stabilization. This condition is due to the fact that said unstable oils retain from their contact with copper reagents, extremely small quantities of oil-soluble copper compounds. These traces of copper compounds remaining in the oil are responsible for the marked acceleration of reactions which lead to the formation in said oil of color, gum, resinous deposits and polymers; these deteriorative changes seriously impair such properties of the oil as color, gum content and octane number.

One object of this invention is to effect the removal of traces of copper compounds from hydrocarbon oils.

Another object of this invention is to prevent the deterioration of hydrocarbon oil which has been treated with copper reagents by the removal from said oil of small amounts of retained oilsoluble coppercompounds responsible for aforesaid deterioration.

A further object of this invention is the production of hydrocarbon oil of good color and stable with respect to gum formation subsequent to treatment with copper-containing reagents.

A further object of this invention is the treatment of oil which retains traces of copper compounds subsequent to sweetening with copper reagents, to remove said copper from the oil,

thereby delaying or preventing deterioration.

Another object of this'invention is to provide a step in the sweetening of hydrocarbon oil with copper reagents whereby the sweetened oil is stabilized against deterioration by the removal therefrom of retained copper salts.

Another object of this invention is the converand/or formation of resinous matter, polymers and oxidation products; that is, a method of stabilizing the oil by bringing it in contact with an alkaline sulphide solution subsequent to treating with the copper reagent.

We have now discovered that copper treated oils may be stabilized by means other than the alkaline sulfide solution referred to above and captide, the next number in the series,

more soluble, yet its actual solubility figure isthat these means involve certain improvements and advantages. This discovery is extremely important in that it clearly defines the conditions which must be met to produce stabilizedoils. This discovery, likewise makes it possible to divide treating agents into two groups, the first group consisting of those reagents which will effectively remove the hydrocarbon oil-soluble copper compounds and thereby stabilize the oil, and the second group consisting of those reagents which will not remove suflicient quantities of the copper compounds to stabilize the oil.

We have found that copper mercaptides increase in solubility in the oil with increasing molecular weight of the mercaptans. Copper methyl mercaptide is the most insoluble of all the copper mercaptides and is almost totally insoluble in hydrocarbon oils. Copper ethyl meris a little extremely lowa Copper butyl mercaptides and amyl mercaptides are much more soluble and their solubilities may be determined in the usual manner of precise measurements.

We have now discovered that hydrocarbon oil' containing copper methyl mercaptide, and therefore completely saturated with respect tothe substancadoes not showany of the undesirable reactions mentioned above as resulting from the catalytic effect of dissolved copper compounds. In other'words, we have established that the con soluble copper methyl centration of copper from a saturated solution of copper methyl mercaptide in hydrocarbon oil is too low to cause deterioration of the oils. On the other hand, we have found that if the hydrocarbon is saturated with'respect to copper ethyl mercaptide, the concentration of copper is just suflicient to cause a slow depreciation in the said properties of the oil. Thus, we have established that there is a critical value for copper concentration in the oil, above which deterioration will occur, and below which the oil will be .stable as regards gum and color formation in storage- This improved process of stabilization depends on the efiective removal of traces of copper compounds from the contaminated hydrocarbon oil by treating said oil to completely convert the hydrocarbon oil-soluble copper compounds into compounds whose solubility is less than the solubility of the copper salt of ethyl mercaptan. By this means, and the subsequent separation of these more insoluble compounds from the hydrocarbon oil, the deterioration due to dissolved copper compounds in the oil is prevented. Since the deterioration of oil is accelerated in a catalytic manner by dissolved copper salts, it follows that copper salts more insoluble than copper ethyl mercaptide are inactive ascatalysts for deteriorative reactions in oil, and likewise possess marked resistance to oxidating processes phosphate solutions, or by the addition to the oil of controlled amounts of ethyl mercaptan.

In order to explain more exactly the criterion by which the stabilization of copper-containin oil is Judged, the relative solubilities of the copper compounds encountered may be' considered.

The sulfides of copper are the most insoluble compounds of the metal. The mercaptides by reason of analogous structure exhibit similar solubilities in water, but are slightly more soluble in oils dueto the organic nature of the alkyl or .aryl group present in the mercaptide molecule.

The sulfides of copper have a solubility of about 0.00033- gram per liter of water and an inflnitesimal solubility in hydrocarbon oils; the solubility of copper methyl mercaptideis approximately 0.000003 gram per liter of cracked naphtha, or about one-hundredth the solubility of copper sulfide in water. These solubility figures are based on extremely sensitive colorimetric tests, especially devised to indicate the presence and concentration of copper in hydrocarbon oil. A

The following table shows the approximate solubilities of copper salts in oils, or the extent to which oil-soluble copper compounds are formed by contact of the oils with said copper salts for a 24 hour period.

Table I v b 0 Copper salt Hydrocarbon oil g f COD 9 ggg gi g Pcrjaper Grams per 1000 cc. million of oil Copper oxide Doctor-sweet cracked naphtha. 0.0003 Sapprox.) Copper carbonate (basic) ..d0 0.0003 approx.) Copper bydroxide 0.0003 (approx.) Copper phosphate 0.0003 (approx.) Copper cyanide (KCN so 0.0003 (approx) Copper silicate 0.0003 (approx.) Copper sulflte 0.0003 (approx.) Copper-n-butyl-mercuptide- 0.0003 (approx) Copper-t-butyl-mercaptidc. 0.300 Copper-ethyl-mercaptide 0.00003 1 Sp. gr. oi naphtha taken as 0.75.

which would change said insoluble copper compounds to more active forms which would be injurious to the oil.

Oil-soluble copper compounds which may be formed in complex hydrocarbon -oil mixtures, particularly in petroleum distillates, are usually mercaptides or salts of acidic components such as cresylic and naphthenic acids: Such compounds may be more soluble than copper ethyl mercaptide, and likewise may not be removed from an oil in which said compounds are dis-, solved unless the method of treating or stabilization forms therewith copper compounds less soluble than copper ethyl mercaptide. For example, after a cracked naphtha has been in con-i tact with copper oxide, copper carbonate or copper phosphate, sensitive tests show the presence of traces of copper remaining in the naphtha, whereas a portion of the same naphtha after prolonged contact with copper methyl mercaptide shows no evidence of dissolved copper compounds. Further, the small amounts of copper saltspresent in a cracked gasoline which has been sweetened with a cupric chloride solution may be removed by adding thereto a controlled amount of methyl mercaptan to convert the more soluble copper compounds into the less mercaptide. Complete is not effected by treattic soda, carbonate or removal of the copper ment of the oil with caus It will be seen from the values listed in Table I that complete removal of copper from an oil may not be accompli with a reagent to form any of the copper salts listed. This fact is based on experimental data which proves that the deterioration of an oil due to dissolved copper is not prevented unless the copper content of said oil is reduced to a value less than 0.1 p. p. m. as shown in Table II.

Thusin order to prevent the deterioration of a hydrocarbon oil which has been treated with a copper-containing reagent, it is necessary to treat said oil in order to reduce the amount of dissolved copper to a value less than 0.1 p. p. m.

This is accomplished according .to our invention by converting the copper present in the oil into shed by contacting said oil compounds with oil solubility less than the oilsolubility of copper-ethyl mercaptide.

As examples of the practice of my invention, the following examples are described:

EXAMPLE I A sample of cracked gasoline which had been sweetened by treatment with a solution containing cupric chloride was separated from the copper reagent and divided into two parts. One part was stored without further treatment. To the other portion was added a solution of methyl mercaptan in sulfur-free hexane solution, the quantity added being sufficient to cause the gas- EXAMPLE III To a sample of doctor sweet cracked gasoline was added solid copper ethyl mercaptide and 5 shaken until the oil was saturated with the oline to have a methyl mercaptan content of 15 given below:

Table III v Color Color No. Gasoline sample Copper test inal tig aster color y storage storage 1 Cracked gasoline-no additional treatment Negative +24 +22 +21 2 Crtagked gasoline-saturated with solid copper-ethyl-mercap- Positive, approx. +24 +16 i e. 1 p. p. m. I 3 #2 sample-added 0.000 per cent methyl mercaptan followed Negative, less +24 +22 +21 by water wash. than 0.1 p. p. m. 4 #2 sample-plus 2 per cent sour vapor recovery gasoline com +24 +21 mining 0.01 per cent methyl mercaptan. 5 #2tsampefiihntimately contacted with alkaline aqueous solu +24 +22 +21 ion 0 l izone. 6 #2 sample-contacted with arnmoniacal solution of alpha- +24 +22 +21 benzoinoxime. #2 sample-contacted with aqueous solution of thional de. +24 +22 +21 #2 sample-contacted with aqueous solution of 6.7-d1bromo- +24 +22 +21 hydroxyquinoline. #2 sample-contacted with ammonlacal solution of diethyldi- +24 +22 +21 thiocarbonate.

0.003 weight per cent. After the addition of the mercaptan, the gasoline was allowed to stand in which deterioration is' for two hours, after which it was washed with water and stored. The results of this stabilizing treatment are shown below:

These samples are illustrative of the manner preventedin hydrocarbon oils containing soluble copper compounds,

according to the practice of this invention and the critical value for allowable copper concen-- Orig" 9 A aft 30 er ppesrance er Gasoline samples Copper test cigfir days, days, storage I storage Cracked gasoline unstsbilized Positive, greater than 1 p. p. m.--. +24 --16 Dark brown, gummy. Cracked gasoline plus 0.003 perv cent Negative, less than 0.1 p. p. m +24 +23 +22 color.

methylmercaptan.

1 This gasoline was doctor sweet; no trace of mereoptan after two days.

EXAMPLEII tration in oil which is stable with regard to color A sample of the same gasoline described in and gumformartionm storage is thus disclosed Example I was similarly treated except that the stabilizing reaction was brought about by the addition to one portion of the gasoline of sufficient sour vapor recovery gasoline to amount to 2 per cent by volume. This vapor recovery gasoline contained approximately .01 weight per cent of methyl mercaptan. -The results of this stabilization are illustrated below:

We claim:

1. In the process of sweetening hydrocarbon oil with copper reagents, the step of stabilizing the sweetened oil to prevent deterioration-due to retained oil .soluble copper salts which comprises adding a small quantity of a stabilizing agent comprising 5.7-dibromohydroxyquinoline.

2. The process in claim 1 in which the stabiliz Ori A rance Gasoline sample Copper test m5 fig are???) days color storage storage 'Crecked gasoline-copper treated-unstabilized. Positive greater than 0.1 p. p. m 24 '-16' Darkb wn. Cracked gmoline-copper treated plus 2 per cent Negative, less than 0.1 p. p. m.... :24 +23 +22 cob a.

(vol.) of sour vapor recovery gasoline.

1 This gasoline was doctor sweet.

ing agent is an aqueous solution of 5.7-dibromo-