GB2373790A

GB2373790A - Sweetening LPG/liquid petroleum distillates using metal phthalocyanine sulphonamide catalyst

Info

Publication number: GB2373790A
Application number: GB0108085A
Authority: GB
Inventors: Bir Sain; Som Nath Puri; Gautam Das; Bhagwati Prasad Balodi; Sunil Kumar; Anil Kumar; Turuga Sundara Rama Prasad Rao; Gur Pratap Rai; Virendra Kumar Kapoor; Virendra Kumar Bhatia
Original assignee: Council of Scientific and Industrial Research CSIR
Current assignee: Council of Scientific and Industrial Research CSIR
Priority date: 2001-03-30
Filing date: 2001-03-30
Publication date: 2002-10-02
Anticipated expiration: 2021-03-30
Also published as: GB0108085D0; GB2373790B

Abstract

The present invention relates to a process for sweetening of liquefied petroleum gas (LPG) and light petroleum distillates by liquid-liquid extraction using metal phthalocyanine sulphonamide catalyst which comprises extracting the mercaptans contained in liquefied petroleum gas (LPG) or light petroleum distillate such as pentanes and light straight run naphtha, by liquid-liquid extraction using an aqueous or alcoholic solution of alkali metal hydroxide of concentration ranging between 1 wt% to 50 wt% in the presence of a metal phthalocyanine sulphonamide catalyst in the concentration ranging from 5 - 4000 ppmw, at a temperature ranging from 10{C to 80{C, at a pressure ranging from 1 kg/cm<SP>2</SP> - 50 kg/cm<SP>2</SP> in a continuous or batch manner, converting the mercaptans present in above said extract into corresponding disulphides by passing air, oxygen or any oxygen containing gas at the above same temperature and pressure, and regenerating the alkali solution containing catalyst for recycling by separating the upper layer of disulphides from said alkali solution of catalyst.

Description

A Process For Sweetening LPG and Light Petroleum Distillats The present invention relates to a process for sweetening of LPG, light petroleum distillates by liquid-liquid extraction using metal phthalocyanine sulphonamide catalyst.

Particularly, the invention relates to a process for sweetening of liquefied petroleum gas (LPG) and light petroleum distillates such as pentanes and light straight run naphtha (LSRN), comprising liquid-liquid extraction of the mercaptans contained therein by alkali solution and regeneration of the mercaptan containing alkali solution by oxygen, using metal phthalocyanine sulphonamide catalyst, whereby the mercaptans are converted to corresponding disulphides and the regenerated alkali solution can be reused for mercaptan extraction.

Metal phthalocyanine sulphonamide catalyst has been prepared by a procedure as discussed and described in our copending Indian patent application No 1032/DEL/2000.

It is known that the presence of mercaptans in petroleum products such as LPG, naphtha, gasoline, kerosene, ATF etc is highly undesirable due to their foul odour and highly corrosive nature. These are also poisonous to the catalysts and adversely affect the performance of tetraethyl lead as octane booster. Although there are several processes known for the removal of mercaptans from petroleum products, the most common practice is to oxidize the mercaptans present, to less deleterious disulphides with air in the presence of a catalyst. Generally, the lower mercaptans present in LPG, pentanes, LSRN and light thermally cracked naphtha are first extracted in alkali solution and then oxidized to disulphides with air in the presence of a catalyst.

The disulphides, being insoluble in alkali solution are separated out from the top and the alkali is regenerated. In the liquid-liquid sweetening the lower mercaptans present in petroleum products like pentanes, LSRN, FCC cracked naphtha etc are converted to disulphides by direct oxidation with air in the presence of alkali solution and catalyst. The higher molecular weight mercaptans present in petroleum products like heavy naphtha, FCC gasoline, ATF and kerosene are oxidized to disulphides with air in a fixed bed reactor containing catalyst impregnated on a suitable support like activated carbon (Catal. Rev. Sci. Eng. 35 (4), 571-609,1993).

It is also well known that the phthalocyanines of the metals like cobalt, iron, manganese, molybdenum and vanadium catalyze the oxidation of mercaptans to disulphides in alkaline medium. Among these cobalt and vanadium phthalocyanines are preferred. As the metal phthalocyanines are not soluble in aqueous medium, for improved catalytic activity their derivatives like sulphonated and carboxylate metal phthalocyanines are used as catalysts for sweetening of petroleum fractions. For example, use of cobalt phthalocyanine mono sulphonate as the catalyst in the fixed bed sweetening of various petroleum products (US Patents No.

3,371, 031; 4,009, 120 ; 4,207, 173; 4, 028, 269; 4,087, 378; 4,141, 819; 4,121, 998; 4,124, 494; 4,124, 531) and cobalt phthalocyanine disulphoante (US Patent No. 4,250, 022) tetra sulphonate (US Patent No. 2,622, 763) and the mixture thereof (US Patent No. 4,248, 694) as catalysts for liquid-liquid sweetening and alkali regeneration in mercaptan extraction of light petroleum distillates has been reported. The use of phenoxy substituted cobalt phthalocyanine as sweetening catalyst (Ger Offen 3,816, 952), cobalt and vanadium chelates of 2, 9, 16, 23-tetrakis (3, 4-dicarboxybenzoyl) phthalocyanine as effective catalyst for both homogeneous and fixed bed mercaptan oxidation (Ger Offen 2,757, 476; Fr. Demande 2,375, 201) and cobalt, vanadium

chelates of tetrapyridinoporphyrazine as active catalysts for sweetening of sour petroleum distillates (Ger Offen 2,441, 648) has also been reported.

It is well known that the catalysts used for the sweetening of LPG and light petroleum distillates like pentanes, LSRN etc. by liquid-liquid mercaptan extraction and alkali regeneration are di-, tri-and tetra sulphonates of metal phthalocyanines particularly those of cobalt and vanadium phthalocyanines; cobalt phthalocyanine sulphonates being specially preferred. The cobalt phthalocyanine sulphonates differ in activity and in their solubility characteristics depending upon the number of sulphonate functionalities, leading to problems in their use as catalysts.

Cobalt phthalocyanine disulphonate, a commonly used catalyst in sweetening of LPG and light petroleum fractions by liquid-liquid mercaptan extraction and alkali regeneration is extremely dusty in the dry fine powder form and causes handling problems. To overcome these problems cobalt phthalocyanine disulphonate is admixed with water and commonly used as a slurry.

However, with insufficient mixing the cobalt phthalocyanine disulphonate precipitates out from the slurry. Moreover, even if the slurry is mixed sufficiently, it retains the cobalt phthalocyanine disulphonate in suspension for a particular length of time only, beyond which the slurry becomes extremely viscous and may form a gel, making it very difficult to remove the material from packaging. Cobalt phthalocyanine tetrasulphonate, on the other hand, is highly soluble in water and its use can eliminate precipitation and gel forming problems associated with the use of cobalt phthalocyanine disulphonate. However, it is reported that cobalt phthalocyanine tetrasulphonate has lower catalytic activity than cobalt phthalocyanine disulphonate (US Patent 4, 885, 268).

In application 1032/des/2000 we reported an improved process for the preparation of metal phthalocyanine sulphonamide catalyst useful for sweetening which obviates the drawbacks as detailed above.

The main objective of the present invention is to provide a process for sweetening of LPG and light petroleum distillates by liquid-liquid extraction and alkali regeneration using a metal phthalocyanine sulphonamide catalyst, which obviates the drawbacks as detailed above.

Accordingly the present invention provides a process for sweetening of LPG and light petroleum distillates by liquid-liquid extraction using metal phthalocyanine sulphonamide catalyst which comprises extracting the mercaptarcontained in LPG and light petroleum distillate such as pentanes and light straight run naphtha, by liquid-liquid extraction using an aqueous or alcoholic solution of alkali metal hydroxide of concentration ranging between I wt% to 50 wt% in the presence of a metal phthalocyanine sulphonamide catalyst in the concentration ranging from 5-4000 ppmw, at a temperature ranging from 10 Oc to 80oC, at a pressure ranging from I kg/cm-50 kg/cm2 in a continuous or batch manner, converting the mercaptans present in above said extract into corresponding disulphides by passing air, oxygen or any oxygen containing gas through the reaction mixture at the above same temperature and pressure and regenerating the alkali solution containing catalyst for recycling by separating the upper layer of disulphides from said alkali solution of catalyst.

In an embodiment of the present invention the metal phthalocyanine sulphonamide catalyst used is selected from the group consisting of cobalt, manganese, nickel, iron, vanadium phthalocyanine sulphonamide and their N-substituted sulphonamide derivatives, most preferably cobalt phthalocyanine sulphonamide.

In an embodiment of the present invention the alkali solution used for mercpatan extraction is selected from aqueous or alcoholic solution of alkali metal hydroxides selected from the group consisting of sodium hydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide, and cesium hydroxide most preferably aqueous solution of sodium and potassium hydroxide.

In yet another embodiment of the present invention the concentration of the alkali solution used is preferably in the range 7% to 25% by weight. In yet another embodiment of the present invention the metal phthalocyanine sulphonamide catalyst used is preferably in the concentration ranging between 10 to 1000 ppmw related to alkaline reagent.

In yet another embodiment of the present invention the conversion of mercaptans to disulphides is effected preferably at 35 C to 60oc.

In yet another embodiment of the present invention the conversion of mercaptans to disulphides is effected preferably at I kg/cm to 15 kg/cm pressure.

In yet another embodiment of the present invention the conversion of mercaptans to disulphides is preferably effected by air.

In still another embodiment of the present invention the regeneration of alkali solution is effected with the mercaptide sulphur ranging from 10 ppmw to 40,000 ppmw in feed stocks. Process Description In the sweetening process described herein, the undesirable mercaptans contained in LPG and light petroleum distillates such as, pentanes and LSRN are extracted with alkali solution containing metal phthalocyanine sulphonamide catalyst through a counter current liquid-liquid extraction.

The sweetened petroleum distillat is then passed through an alkali settler and sand filter to remove entrained alkali. The mercaptan and catalyst containing alkali solution obtained from the extractor is oxidized by oxygen or oxygen containing gas like air in an oxidizer whereby the mercaptans present in alkali solution are converted into corresponding disulphides and alkali is regenerated. The disulphlde oil, being insoluble, separates from the alkali solution as an upper layer and is drained. The regenerated alkali solution is reused for mercaptan extraction.

In the sweetening process with this catalyst system extraction of mercaptans from light petroleum distillates can be effected at 10DC to 80 C but the preferred range is lODe to 40oc.

The extraction can be effected at a pressure from ambient to 50 kg/cm2 or more with the preferable pressure range ambient to 20 kg/cm2. The alkali solution used in the extraction is aqueous/alcoholic solution of alkali metal hydroxide such as sodium hydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide, cesium hydroxide, aqueous solution of sodium hydroxide and potassium hydroxide being preferred. The concentration of the alkali solution used is 1% to 50% the preferred range being 7 to 25%.

The sweetening process is effected with a metal phthalocyanine sulphonamide catalyst such as cobalt, manganese, nickel, iron and vanadium phthalocyanine sulphonamide and their N substituted derivatives, the preferred catalyst is cobalt phthalocyanine sulphonamide. The catalyst is used in the concentration 4 to 1000 ppmw related to alkali solution, the preferred range is 10-1000 ppmw.

The regeneration of mercaptan-containing alkali solution with metal phthalocyanine sulphonamide catalyst is effected at ambient to 90 C temperature. The preferred range being 35 C to 60oc.

The regeneration of alkali solution is effected at atmosphere to 50 Kg/cm2 pressure, the preferred range being 1-15 Kg/cm2.

The regeneration of alkali solution is effected by air, oxygen or any other oxygen containing gas, air being especially preferred. The following examples are given by way of illustration and therefore should not be construed to limit the scope of the invention.

Example 1 Preparation of Cobalt Phthalocyanine Sulphonamide Catalyst as described in Patent Application no. 1032/de/2000 Preparation of Cobalt Phthalocyanine Sulphonyl Chloride For the preparation of cobalt phthalocyanine sulphonyl chloride, 30 parts by weight of cobalt phthalocyanine were slowly added with stirring to 315 parts by weight of chlorosulphonic acid. The reaction mixture was heated to about 75 C in one hour and from 75 C to about 130oC in 1.5 hours by controlling the heating rate, with constant stirring. The reaction mixture, after

maintaining 130-135OC for additional 4 hours, was cooled to 60-65OC, and then 123 parts of thionyl chloride were slowly added. The contents were heated to 79 C and maintained at this temperature for one hour. The reaction product was cooled to room temperature and slowly added to crushed ice, keeping the temperature preferably below 5 C. The precipitated cobalt phthalocyanine sulphonyl chloride was filtered and washed thoroughly with cold water. The filtered cake was stored wet at 0 C until required.

Preparation of Cobalt Phthalocyanine Sulphonamide In a typical preparation of cobalt phthalocyanine sulphonamides, a wet cake of cobalt phthalocyanine sulphonyl chloride was dispersed in 900 parts of ice water and 190 parts of methanol were added to give a homogeneous dispersion. The reaction mixture was stirred at 5-8OC and anmoma gas was passed through the mixture until the pH was fairly alkaline (pH 8-9). Pyridine (1.2 parts) was then added and the mixture stirred at room temperature for 20 minutes. This was followed by addition of 6 parts of 10% sodium hydroxide solution followed by stirring the reaction mixture for 40 minutes at room temperature. The contents were then heated to 80 C and after maintaining at this temperature for I hour, cooled to room temperature and poured over a mixture of ice and concentrated hydrochloric acid keeping the pH fairly acidic (2-3). The precipitated cobalt phthalocyanine tetrasulphonamide was filtered, washed thoroughly with cold water and dried in vacuum oven to yield 44 g of the product. The FAB mass spectral analysis of the sulphonamide obtained using cobalt phthalocyanine as the starting material showed the presence of tetra sulphonamide as the major product, followed by trisulphonamide and disulphonamide isomers.

Example 2 Alkali Regeneration in LPG Mercaptan Extraction As the metal phthalocyanine sulphonamide catalyst has no effect an mercaptan extraction from LPG, but only catalyses the oxidation of mercaptide to disulphide to regenerate the alkali solution used for extraction, the experiments were designed to study regeneration of alkali solution using ethane thiol mercaptan as the model mercaptan.

In the model experiments the calculated amount of ethyl mercaptan was added to light naphtha.

Themercaptan sulphur content was estimated by UOP method 163-89. Thus prepared feed was taken in a round bottom flask. The mercaptan present in naphtha was extracted with 14% aqueous sodium hydroxide solution containing 200 ppmw of the catalyst with stirring under inert atmosphere. After extraction the mercaptan sulphur content of naphtha was estimated. The spent alkali thus obtained was regenerated by passing air into it. The alkali regeneration time (as indicated by reappearance of the blue colour in the solution) was monitored in repeated experiments by reusing the same catalyst solution. The strength of the sodium hydroxide solution was also monitored. The mercaptide sulphur content of the regenerated sodium hydroxide solution was found to be below 1 ppmw by the above method (UOP 163-89) throughout the entire study, showing complete alkali regeneration. Results are given in Table-1.

Table-1

Mercaptan sulphur in feed,'S'ppmw 1500 Catalyst concentration in alkali ppmw 200 .

Volume of alkali taken for extraction 50 ml

Volume of feed Cumulative Mercaptan in Alkali NaSR in treated with volume of feed extracted feed regeneration regenerated alkali ml treated ml'S'ppmw time, min alkali ppmw 300 300 < 5 10.5 < 1 300 600 < 5 12.0 < 1 300 900 < 5 12.0 < 1 300 1200 < 5 15.0 < 1 300 1500 < 5 15.0 < 1 150 1650 < 5 12.0 < 1 Example 3 Alkali Regeneration in LPG Mercaptan Extraction Using a Glass Column Apparatus As the metal phthalocyanine sulphonamide catalyst has no effect an mercaptan extraction from LPG, but only catalyses the oxidation of mercaptide to disulphide to regenerate the alkali solution used for extraction, experiments were designed to study regeneration of alkali solution ethane thiol as the model mercaptan. The laboratory apparatus consists of a glass column with air inlet at the bottom connected to air cylinder through a control valve. A calculated amount of ethane thiol was added to 14 % aqueous sodium hydroxide containing 200 ppmw metal phthalocyanine sulphonamide catalyst, and the mercaptan sulphur content was estimated by UOP method 163-89. The mixture was then transferred to the glass column and oxidized by passing air until all the ethyl mercaptide was converted to dlsulphide, indicated by the appearance of blue colour. Thus formed, diethyl disulphide clearly separated from the catalyst-containing alkali solution in an upper layer. The conversion of mercaptide to disulphide was monitored by analyzing the mercaptide concentration in the \reaction mixture at different intervals. The results are given in Table-2.

Table-2

Mercaptan sulphur in 14 % sodium hydroxide solution ppmw 3307 Concentration of the catalyst in alkali solution ppmw 200 Total volume of reaction mixture, taken ml : 230 Air rate, lit/min : 0.8

Time, min Mercaptan'S', ppmw Conversion, wt% 0 3307 0 1 2816 14.85 5 45 98.64 8 0 100.00 Example 4 Alkali Regeneration in LPG Mercaptan Extraction Using a Glass Column The procedure followed the experimental details were as described in Example 3. The results obtained are presented in Table-3.

Table-3 Mercaptan sulphur in 14 % sodium hydroxide solution ppmw : 8533 Concentration of the catalyst in alkali solution ppmw : 200 Total volume of reaction mixture, taken mi : 230 Air rate, lit/min : 0.83

Time, min Mercaptan'S', ppmw Conversion, wt% 0 8533 0 1 6220 27.11 5 5042 40.91 10 1833 78.52 150100. 00 Example 5 Alkali Regeneration in LPG Mercaptan Extraction Using a Glass Column Apparatus The procedure followed the experimental details were as described in Example 3. The results obtained are presented in Table-4.

Table-4 Mercaptan sulphur in 14 % sodium hydroxide solution ppmw 13129 Concentration of the catalyst in alkali solution ppmw : 200 Total volume of reaction mixture, taken ml 230 Air rate, lit/min 0. 8

Time, min Mercpatan'S', ppmw Conversion, wt% 0 0 13129 0 1 12251 6.69 10 7337 44. 12 20 1101 91. 61 25 0 100. 00 Example 6 Alkali Regeneration in LPG Mercaptan Extraction Using a Glass Column Apparatus The procedure followed the experimental details were as described in Example 3. The results obtained are presented in Table-5.

Table-5 Mercaptan sulphur in 14 % sodium hydroxide solution ppmw: 17626 Concentration of the catalyst in alkali solution ppmw: 200 Total volume of reaction mixture, taken ml 230 Air rate, lit/min 0. 75

Time, min Mercaptan'S', ppmw Conversion, wt% 0 17626 0 1 16663 5.46 10 8140 53.82 20 1664 90.56 29 0 100.00 Advantages of the Invention

The main advantages of the present invention over the previous inventions are : (a) The present invention provides a process for sweetening of LPG and light petroleum distillates such as pentanes and light straight run naphtha (LRSN) by liquid-liquid extraction and alkali regeneration using a metal phthalocyanine sulphonamide catalyst.

(b) The metal phthalocyanine sulphonamide catalysts used in the present invention are found to be highly active for alkali regeneration in the sweetening of LPG and light petroleum distillates.

(c) Metal phthalocyanine sulphonamide catalysts used in the present invention are not dusty and do not create handling problems as encountered with the conventional cobalt phthalocyanine disulphonate catalysts. Therefore, admixing with water to make a slurry is not required.

(d) As the metal phthalocyanine sulphonamides used as catalysts in this invention are insoluble in acidic media their isolation is easier than conventional cobalt phthalocyanine sulphonate catalysts.

Claims

We Claim

1. A process for sweetening of LPG and light petroleum distillates by liquid-liquid extraction using a metal phthalocyanine sulphonamide catalyst comprising: extracting the mercaptans contained in LPG or light petroleum distillate such as pentanes and light straight run naphtha by liquid-liquid extraction using an aqueous or alcoholic solution of alkali metal hydroxide of concentration ranging between 1 wt% to 50 wt%, in the presence of a metal phthalocyanine sulphonamide catalyst in a concentration ranging from 5-4000 ppmw, at a temperature ranging from 10 C to 80oC, at a pressure ranging from 1 kg/cm2 to 50 kg/cm2, in a continuous or batch manner; converting the mercaptans present in the above said extract into corresponding disulphides by passing air, oxygen or any oxygen containing gas through the reaction mixture at the above same temperature and pressure; and regenerating alkali solution containing catalyst by separating the upper layer of disulphides from said alkali solution of catalyst.

2. A process as claimed in claim 1, wherein the metal phthalocyanine sulphonamide catalyst used is selected from the group consisting of cobalt, manganese, nickel, iron, vanadium phthalocyanine sulphonamide and their Nsubstituted sulphonamide derivatives, most preferably cobalt phthalocyanine sulphonamide.

3. A process as claimed in any of claims 1 or 2 wherein the alkali solution used for mercaptan extraction is an aqueous or alcoholic solution of alkali metal hydroxide wherein the alkali metal hydroxide is selected from the group consisting of sodium hydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide and cesium hydroxide, most preferably an aqueous solution of sodium and potassium hydroxide.

4. A process as claimed in any one of claims 1 to 3 wherein the concentration of the alkali solution used is preferably in the range 7% to 25% by weight.

5. A process as claimed in any one of claims 1 to 4 wherein the metal phthalocyanine sulphonamide catalyst used is preferably in the concentration ranging between 10 to 1000 ppmw related to alkaline reagent.

6. A process as claimed in any one of claims 1 to 5

wherein the conversion of mercaptans to disulphides is effected preferably at 35 C to 60oC.

7. A process as claimed in any one of claims 1 to 6 wherein the conversion of mercaptans to disulphides is effected preferably at 1 kg/cm2 to 15 kg/cm2 pressure.

8. A process as claimed in any one of claims 1 to 7 wherein the conversion of mercaptans to disulphides is preferably effected by air.

9. A process as claimed in any one of claims 1 to 8 wherein the regeneration of alkali solution is effected with the mercaptide sulphur ranging from 10 ppmw to 40,000 ppmw in feed stocks.

10. A process for sweetening of LPG and light petroleum distillates by liquid-liquid extraction using a metal phthalocyanine sulphonamide catalyst substantially as hereinbefore described with reference to the examples.