US3063935A

US3063935A - Hydrocarbon sweetening process

Info

Publication number: US3063935A
Application number: US53372A
Authority: US
Inventors: Willem E Nieuwenhuis
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1959-09-08
Filing date: 1960-09-01
Publication date: 1962-11-13
Anticipated expiration: 1979-11-13

Description

this corrosiveness.

nited States Patent 3,063,935 HYDROCARBON SWEETENING PROCESS Willem E. Nieuwenhuis, The Hague, Netherlands, as-

signor to Shell Oil, Company, a corporation of Delaware No Drawing. Filed Sept. 1, 1960, Ser. No. 53,372

Claims priority, application Netherlands Sept. 8, 1959 9 Claims. (Cl. 203-204) This invention deals with the removal of mercaptans from liquid hydrocarbons, and more particularly relates to the preparation of substantially non-corrosive, mercaptan-free, hydrocarbon oil.

It is known to free light hydrocarbon oils, such as gasoline and kerosene, from mercaptans by treating these oils with an aqueous alkali metal hydroxide solution. In this treatment the mercaptans are extracted by the alkali.

metal hydroxide solution and converted into mercaptides.

If desired, this treatment may be carried out in the presence of oxygen, in which case the mercaptides are oxidized to disulfides. The latter are oil-soluble and pass from the aqueous alkali metal hydroxide solution to the hydrocarbon oil.

In order to increase the extractive power of the'alkali metal hydroxide solution, a solubility promoter, a solutizer, may be dissolved in the solution. Examples of suitable solutizers are amino and hydroxyl alkyl amines in which the alkyl groups contain 2 to 3 carbon atoms, glycols, amino glycols and diamino glycols having from 3 to 5 carbon atoms, diamino, dihydroxy or amino hydroxy dialkyl ethers or thioethers in which the alkyl groups contain 2 or 3 carbon atoms, alkali metal salts, in particular potassium salts, of fatty acids having from 3 to 5 carbon atoms, such as isobutyric acid, or hydroxy or amino fatty acids having from 4 to 7 carbon atoms, or phenyl acetic acid, or hydroxy phenyl acetic acid or amino phenyl acetic acid, alkyl phenolates, and mixtures of two or more of the above compounds.

If the mercaptan removal is carried out in the presence of oxygen, it is known that aqueous alkali metal hydroxide solutions containing a phenolate as a solutizer may be employed, thereby increasing the extractive power of the solution for mercaptans. It may also be advisable to 'add an auxiliary substance to the alkali metal hydroxide solution in order to promote the solvent for oxygen. For examples, alkali metal hydroxide solutions containing solutizers are used which contain acetic acid and formic acid to increase the solvent power for oxygen.

The processes discussed above are generally not carried out to the extent where all mercaptans are removed from the hydrocarbon oil. For practical purposes it is suflicient to reduce the mercaptan content so that the treated product is free from any offensive mercaptan odors, for example, a mercaptan sulfur content of less than 20 ppm. would be satisfactory.

The processes set forth above, while quite effective in For example, when treated in accordance with the above method, a hydrocarbon oil would be substantially mercaptan-free while having a marked corrosive tendency towards copper even where the parent product was noncorrosive.

It is a principal object of this invention to eliminate tion in corrosiveness is achieved by adding a quantity of mercaptan-containing hydrocarbon oil, which is non-copper-corrosive, to the mercaptan-free hydrocarbon oils A which have been treated in accordance with the abov processes.

The invention therefore relates to a process for the It has been discovered that a reducice preparation of a substantially mercaptan-free, light hydrocarbon oil which is not corrosive to copper, by treating a light hydrocarbon oil containing mercaptans with an aqueous alkali metal hydroxide solution, which may contain one or more solutizers to increase the extractive power for mercaptans to reduce the mercaptan content to a small amount and adding a quantity of a mercaptancontaining hydrocarbon oil which is non-copper-corrosive to the treated light hydrocarbon oil to produce a blended product which is non-corrosive to copper.

In the present specification the hydrocarbon oil is termed corrosive to copper, viz., copper positive, when the corrosion test according to A.S.T.M. method D130, i.e., the copper strip corrosion test, is classified as 2A or lower. The hydrocarbon oil is considered non-coppercorr-osive, viz., copper negative, when the result of the corrosion test is classified as 1B or higher.

It follows from two tests set forth below that compounds with oxidizing properties are not responsible for the corrosiveness. The starting material used in the first test was a catalytically' cracked gasoline pre-washed with a caustic alkali solution in order to remove hydrogen sulfide and the like and with a mercaptan sulfur content of 74 ppm. This gasoline was successively subjected to 4 extractions with an aqueous caustic alkali solution containing 650 g./l. of potassium hydroxide and g./l. of cresol (as cresolate). The copper strip corrosion test (A.S.T.M. method D) gave the following results:

Mercaptans, Copper Number of Extractions p.p.m. Strip 8 2B2C 4 2A 2 1B It was found that the original gasoline which was noncopper-corrosive, viz., copper negative (1A) has become copper positive (2C) after the first extraction and'remained so after the second and third extraction, but after the fourth extraction the gasoline had'become copper negative lB) again. This test showed that the gasoline originally contained corrosive compounds which apparently were inhibited by compounds subsequently preferentially extracted by the caustic alkali solution. When the extraction was continued it was found that the corrosive compounds were removed as well; the mercaptan content, however, is then also reduced to practially nil (2 p.p.m.).

This test, which was carried out in the absence of an oxidizing agent, shows that the corrosive properties which the hydrocarbon oil exhibits after an extractive mercaptan reduction are attributable to compounds with oxidizing properties. in order to demonstrate'this a second test was carried out with a copper-positive gasoline obtained by treating a copper-negative gasoline, in the presence of oxygen, with an aqueous alkali metal hydroxide solution containing a solutizer to increase the extractive power for mercaptans. When adding copper-negative gasoline containing mercaptans to the treated copperpositive gasoline a copper-negative mixture was obtained. The analytically determined mercaptan content showed that in the mixture no mercaptans were converted, which would have been the case if compounds with oxidizing properties had been present in the copper-positive portion.

The present invention is therefore based on the new and surprising insight that a copper-negative light hydrocarbon oil containing mercaptans may naturally contain copper-corrosive compounds which are inhibited by materials originally present in the hydrocarbon oil. When the mercaptans are extracted by means of an aqueous alkali metal hydroxide solution these inhibiting compounds are found to be preferentially extracted, thereby disturbing the ratio of copper-corrosive compounds to inhibiting compounds and causing the copper-negative hydrocarbon oil to become copper-corrosive. Since the copper-corrosive compounds are also extracted simultaneously, although to a lesser extent, it is possible to eliminate the copper corrosiveness of a hydrocarbon oil substantially free from mercaptans by adding a relatively small quantity of copper-negative hydrocarbon oil.

It should be noted that it is not known what compounds are responsible for the corrosive or the inhibiting properties, although it follows from the above that these compounds are very similar to the aliphatic mercaptans, as far as their extractive behavior with respect to an aqueous alkali metal hydroxide solution is concerned, the inhibiting compounds being found to be more readily extractable than the corrosive compounds.

The present copper-corrosiveness is not caused by free sulfur, as shown by the following test calried out with a copper-positive gasoline used'as a starting material in the second test described above. This gasoline contained 17 p.p.m. of'mercaptan sulfur and showed a copper strip 23. After treatment with a sodium sulfide solution to remove any free sulfur present both the mercaptan sulfur content and the copper strip were found to be unaltered.

disclosed by the first test described above, it is possible to prepare a copper-negative hydrocarbon oil by subjecting the starting hydrocarbon oil to a sufficiently drastic extraction treatment wherein the resulting mercaptan-sulfur content is practically nil (2 p.p.m.) Since all types of mercaptans are not equally as readily extractable, with the tertiary mercaptans in particular being very diflicult to remove, it is neither attractive nor practical to attempt such a treatment of the hydrocarbon oil in the refinery. This would necessitate a much larger installation and a considerably longer treatment. As regards the practical requirements with respect to the mercaptan-sulfur content of light hydrocarbon oils, removal to a level of approximately -20 p.p.m. is generally suflicient. Such a partial removal of mercaptans can be efiected in a considerably simpler manner and according to the present invention, this removal need only be carried out to such an extent that the final mercaptansulfur content of the copper-negative mixture, obtained by adding a quantity of non-corrosive mercaptan-containing hydrocarbon oil to a hydrocarbon oil partly freed from mercaptans, does not exceed the above-mentioned limit of approximately 5-20 p.p.m. and is thus free of an offensive mercaptan odor.

The non-copper-corrosive starting hydrocarbon oil will generally be used as inhibiting agent for the coppercorrosive hydrocarbon oil which is partly free from mercaptans, although other coppernegative hydrocarbon oils may be used. Particularly suitable mercaptan-containing hydrocarbon oils are those obtained by straight-run distillation. The use of an oil other than the starting hydrocarbon .oil may lead to technical and economic advan- V tages, for instance when a quantity of a copper-negative,

mercaptan-containing butane and/ or butylene fraction (socalled C fraction) and/or pentane and/ or pentane-conraining fraction (so-called C fraction) is added to a copper-positive gasoline. The addition of such fractions is often necessary in the refinery to obtain a sufficiently volatile motor gasoline; in this case the mercaptans are previously completely or partly removed from these fractions. The addition of a C and/or C fraction containing mercaptans as inhibiting agent may therefore make it unnecessary to use a separate installation for the removal of the mercaptans from these fractions.

In treating a copper-negative hydrocarbon oil with an aqueous alkali metal hydroxide solution the inhibiting components are preferentially extracted from the hydrocarbon oil and the extract phase will contain a relatively high concentration of inhibiting components. It may therefore be advantageous to introduce a portion of the extract as inhibitor in place of the starting hydrocarbon oil. A mixture of a non-copper-corrosive hydrocarbon oil and an extract may also be used as the inhibiting agent.

The phenomenon of copper-corrosiveness of a light hydrocarbon oil after a treatment with an aqueous alkali metal hydroxide solution is more pronounced in hydro carbon oils obtained by cracking. It occasionally occurs that the light hydrocarbon oil is copper-corrosive even before the extractive treatment for the removal of mercaptans. A starting product of this nature cannot be used to eliminate the copper-corrosiveness of the oil treated with an aqueous alkali metal hydroxide solution. In this case it will be necessary to use a different light hydrocarbon oil containing mercaptans, which is actually copper-negative, or an extract therefrom. The occurrence of copper-corrosive hydrocarbon oils prior to mercaptan extraction indicates that differences may also be expected in the copper-negative starting oils with respect to the content of inhibiting components, viz., the content of corrosive components. It therefore follows that it will be necessary to determine experimentally in each particular case the quantity of untreated hydrocarbon oil, or of inhibiting extract respectively, necessary to modify the copper-positive product into a copper-negative oil.

It has been found that in most cases a copper-negative final product may be obtained by mixing the product which is partly freed from mercaptans with less than 30% by volume of a non-copper-corrosive hydrocarbon oil containing mercaptans. This determines the extent of mercaptanremoval necessary to give a fiinal product which has the desired mercaptan content after addition of less than 30% by volume of the non-copper-corrosive hydrocarbon oil. If, for instance, parts by volume of alight hydrocarbon oil containing 50 p.p.m. of mercaptan sulfur is used as starting material, it will be necessary to desulfurize this oil to 10 p.p.m. in order to obtain a final product with a content of 15 p.p.m. of mercaptan sulfur after addition of 10 parts by volume of the starting hydrocarbon oil. In many cases a copper-negative final product may be obtained by adding 1-20% by volume of a non-copper-corrosive hydrocarbon oil containing mercaptans and as a rule the quantity to be added will vary from 6 to 12% by volume. Instead of non-copperco'rrosive hydrocarbon oil, a corresponding quantity of extract from a non-copper-corrosive hydrocarbon oil may be added; will be appreciated that a mixture of the noncopper-corrosive hydrocarbon oil and an extract may also be employed.

The process may be applied to light hydrocarbon ds (viz., hydrocarbon oils with a boiling range of 40-350 in particular mercaptan-containing gasolines and kerosenes of different origin. For example, gasoline and kerosene obtained by straight-run distillation of crude oil and gasoline and kerosene produced by thermal or catalytic cracking of heavier feedstocks.

It is a preferred embodiment of this invention to remove first any acids present in the hydrocarbon oils by means of a dilute aqueous alkali metal hydroxide solution. These acids are stronger than the mercaptans and are removed before the mercaptans according to the process of the present invention. A pretreatment with dilute caustic alkali solution has an additional advantage in that any thiophenols which may be present and possess a considerably stronger acidic character than aliphatic mercaptans, are removed, at least in a considerable quantity, from the hydrocarbon oil prior to treatment. Since thiophenols occur especially in light hydrocarbon oils obtalned by orackingheavier hydrocarbons, and particularly in products obtained by catalytic cracking, a pretreatment with dilutecaustic alkali solution is especially suitable for such products. This pretreatment is preferably carried out before the cracked products come into contact with oxygen or an oxygen-containing gas to prevent possible gum formation.

The removal of mercaptans from hydrocarbon oils by means of an equeous alkali metal hydroxide solution in the presence of oxygen results in the formation of disulfides which pass into the hydrocarbon oil. Therefore this process is primarily suitable for treating hydrocarbon oils with a low mercaptan content, i.e., lower than 500 p.p.m. and preferably lower than 200 p.p.m., calculated as mercaptan sulfur. In this instance the quantity of disulfides taken up in the hydrocarbon oil would be relatively low.

When a hydrocarbon oil with a considerable mercaptansulfur content, for instance 500 p.p.m. or more, is to be freed from mercaptans, it is possible first to remove the greater portion of the mercaptans, together with other sulfur compounds, by means of an aqueous alkali metal hydroxide solution, which may or may not contain one or more solutizers to increase the extractive power for mercaptans, and then to reduce the mercaptan content by converting them, in the presence of oxygen, into disulfides by means of an alkali metal hydroxide solution which may contain one or more auxiliary substances and solutizers.

When the process carried out in the presence of oxygen is applied to catalytically cracked hydrocarbon oils containing unsaturated compounds, an anti-oxidant is preferably added to the oil to prevent gum formation by the unsaturated components of the oil. In general a quantity of 1200 p.p.m. of such an anti-oxidant is sufficient.

Example I The starting material was a catalytically cracked gasoline with a boiling range of 40-165 C. (A.S.T.M.) and containing 100 p.p.m. of thiophenol sulfur, 50 p.p.m. of alkyl phenols and 90 p.p.m. of alkyl mercaptan sulfur. This gasoline was treated with 1% by volume of a 20% aqueous sodium hydroxide solution at a temperature of 30 C. to remove the thiophenols and a portion of the alkyl phenols. After this treatment the thiophenol sulfur content was nil, the alkyl phenol content 35 p.p.m. and the alkyl mercaptan sulfur content 70 p.p.m. The gasoline, which was copper-negative (copper strip corrosion test 1A), was then passed into a propeller mixer at a temperature of 30 C. in a quantity of 1600 tons/day, the impeller speed being 400 rpm, 32 0 tons/day of treating liquid consisting of 35% by weight of technical cresol, 33% by weight of potassium hydroxide and 34% by weight of water were also continuously supplied to this propeller mixer. In addition, air was blown into the gasoline supply line in a quantity corresponding to 200% of the quantity of oxygen theoretically required for the oxidation of the mercaptans present.

The mixture of gasoline and aqueous solution discharged from the mixer was passed into a settling space in which the two phases separated. The aqueous solution was continuously recycled to the mixer. The separated gasoline, which was copper-positive (copper strip corrosion test 2C) and contained 11 p.p.m. of mercaptan sulfur, was continuously discharged from the settling space and mixed with 1 60 tons/day of the starting gasoline from which the thiophenols had been removed 'by a pretreatment with aqueous sodium hydroxide solution (as above). The resultant gasoline mixture was copper-negative (copper strip corrosion test 1A) and contained 16 p.p.m. of mercaptan sulfur.

Example 11 A catalytically cracked gasoline was treated in the same manner as described in Example I and 'had a copper strip test value of 1A after washing with a 20% aqueous sodium hydroxide solution and a mercaptain sulfur content of 61 p.p.m. The gasoline discharged from the settling space had a copper strip 2B and a mercaptan sulfur content of 17 p.p.m.

After addition of 5% by volume of the starting product washed with sodium hydroxide solution, the mixture had a copper strip lA-lB and a mercaptan sulfur content of 10 p.p.m.

Example III 1% by volume of a gasoline obtained by thermal cracking was added to the same gasoline as in Example II which, after the treatment for removing mercaptans,

showed a copperstrip 2B and had a mercaptan sulfur content of 17 p.p.m. After washing with 20% sodium hydroxide solution this gasoline had a copper strip 1A and a mercaptan sulfur content of 3 p.p.m.

After addition of this gasoline the mixture had a copper strip 1A and a mercaptan sulfur content of 20 p.p.m.

I claim as my invention:

1. A process for preparing a substantially mercaptanfree, non-copper-corrosive light hydrocarbon oil, comprising treating a light hydrocarbon oil, containing mercaptans, with an aqueous alkali metal hydroxide solution containing a solutizer for mercaptans and subsequently separating the treated light hydrocarbon oil, substantially free of mercaptans and displaying copper corrosiveness, from the alkali solution andadding a suflicient amount of a non-copper-corrosive, light hydrocarbon oil containing mercaptans to the treated hydrocarbon oil to produce a substantially mercaptan-free light hydrocarbon oil showing no corrosiveness to copper.

2. The process of claim 1 wherein the treatment with the aqueous alkali metal hydroxide solution is carried out in the presence of oxygen and wherein the hydroxide solution contains an additional substance to promote the solvent power for oxygen.

3. The process of claim 1 wherein the starting material is used as the non-copper-corrosive hydrocarbon oil containing mercaptans which are added to the treated hydrocarbon oil.

4. The process of claim 1 wherein an extract from a non-copper-corrosive straight-run hydrocarbon oil containing mercaptan is the material added to the treated hydrocarbon oil.

5. The process of claim 1 wherein a non-copper-corrosive, hydrocarbon oil containing mercaptans which has been treated with a dilute aqueous alkali metal hydroxide solution to remove hydrogen sulfide and thiophenols, is the material added to the treated hydrocarbon oil.

6. The process of claim 1 wherein 1 to 20% by volume of a non-copper-corrosive, hydrocarbon oil containing mercaptans is the quantity of material added to the treated hydrocarbon oil.

7. The process of claim 1 wherein 1 to 20% by volume of an extract of a non-copper-corrosive, hydrocarbon oil containing mercaptans is the quantity of material added to the treated hydrocarbon oil.

8. The process of claim 1 wherein 6 to 12% by volume of a non-copper-corrosive hydrocarbon oil containing mercaptans is the quantity of material added to the treated hydrocarbon oil.

9. The process of claim 1 wherein the light hydrocarbon oil containing mercaptan used as a starting material is obtained by catalytic cracking.

References Cited in the file of this patent UNITED STATES PATENTS

Claims

1. A PROCESS FOR PREPARING A SUBSTANTIALLY MERCAPTANFREE, NON-COPPER-CORROSIVE LIGHT HYDROCARBON OIL, COMPRISING TREATING A LIGHT HYDROCARBON OIL, CONTAINING MERCAPTANS, WITH AN AQUEOUS ALKALI METAL HYDROXIDE SOLUTION CONTAINING A SOLUTIZER FOR MERCAPTANS AND SUBSEQUENTLY SEPARATING THE TREATED LIGHT HYDROCARBON OIL, SUBSTANTIALLY FREE OF MERCAPTANS AND DISPLAYING COPPER CORROSIVENESS, FROM THE ALKALI SOLUTION AND ADDING A SUFFICIENT AMOUNT OF A NON-COPPER-CORROSIVE, LIGHT HYDROCARBON OIL TO PRODUCE ING MERCAPTANS TO THE TREATED HYDROCARBON OIL TO PRODUCE A SUBSTANTIALLY MERCAPTAN-FREE LIGHT HYDROCARBON OIL SHOWING NO CORROSIVENESS TO COPPER.