CLIAMS:1. A process for obtaining di-sulfide oil having sodium level below 0.1 ppm, said process comprising passing a stream comprising di-sulfide oil having sodium level of 1 ppm through an alumina bed packed in a column, at a liquid hourly space velocity (LHSV) ranging from 0.5 to 5.0 hr-1 and at a pre-determined temperature to obtain a treated stream comprising di-sulfide oil having sodium level below 0.1 ppm.

2. The process as claimed in claim 1, wherein the liquid hourly space velocity (LHSV) ranges from 0.5 to 2 hr-1.

3. The process as claimed in claim 1, wherein the liquid hourly space velocity (LHSV) ranges from 1.0 to 1.5 hr-1.

4. The process as claimed in claim 1, wherein said pre-determined temperature varies from 10 to 40 oC.

5. The process as claimed in claim 1, wherein said pre-determined temperature varies from 20 to 30 oC.

6. The process as claimed in claim 1, wherein the stream comprising the di-sulfide oil having sodium level of 1 ppm is a waste or a by-product stream collected from LPG desulfurization units.

7. The process as claimed in claim 1, wherein the treated stream comprising di-sulfide oil has sodium level below 0.05 ppm.

8. The process as claimed in claim 1, wherein the treated stream comprising di-sulfide oil has sodium level below 0.02 ppm.
9. The process as claimed in claim 1, wherein the treated stream comprising di-sulfide oil has sodium level of 0.01 ppm.

10. The process as claimed in claim 1, wherein the di-sulfide oil is an organic di-sulfide comprising at least one alkyl sulfide selected from the group consisting of dimethyldisulfide, ethylmethyl disulfide and diethyl disulfide.

11. The process as claimed in claim 1, wherein the alumina is characterized by the following properties: average particle size ranging from 0.3 to 0.7 mm; pore volume ranging from 44.1 to 71.9 cm3/100g; surface area ranging from 195 to 331 m2/g; and density ranging from 543 to 829 kg/m3.
,TagSPECI:FIELD OF THE DISCLOSURE:
The present disclosure relates to a process for obtaining di-sulfide oil having sodium level below 0.1ppm.

BACKGROUND:
Di-sulfide oil (sulfur oil) is a low value by-product of Liquefied Petroleum Gas (LPG) desulfurization process. During LPG desulfurization process, LPG laden with mercaptan is treated with NaOH solution in the presence of a homogeneous catalyst to extract mercaptans from the LPG. The di-sulfide oil which is produced as a waste or as a by-product stream during the LPG desulfurization process comprises a relatively high concentration of sodium which makes the di-sulfide oil inappropriate for a number of applications. The relatively high concentration of sodium may be due to the presence of unreacted R-S-Na or due to micro-emulsion formation of R-S-S-R with NaOH solution. The di-sulfide oil obtained from the LPG desulfurization process is sent to a hydrotreater for further processing as a low value stream. Notwithstanding the fact that the di-sulfide oil comprises a relatively high concentration of sodium, the presence of a minimum of 60% sulfur makes it a potential substitute for a number of sulfur containing high value chemical compounds which are used in a number of applications. However, the presence of a relatively high concentration of sodium prevents its use in other applications.

EXISTING KNOWLEDGE:
Among the miscellaneous applications known for sulfur containing compounds, their use as an additive for reducing/preventing the formation of coke on the surface of metallic coils of cracking reactors is a highly desirous application. Further, their use as a sulfiding /pre-sulfiding agent for catalysts used in hydrocrackers and hydrotreaters in refineries and in the hydro-processing of non-edible vegetable oils to produce biofules is also well-known. Among various sulfur containing compounds known to be used as anti-coking additives and/or sulfiding agents, the use of dialkyl sulfide and dialkyl disulfides is well known. However, the major disadvantage allied with the use such compounds is their high cost. Further, proper care is also recommended for commercial trials thereof so as to avoid their detrimental effects on the downstream processes.
A PCT Publication No. 2005/111175 discloses the use of sulfur oil which is a mixture of organic disulfides having C2-C4 for inhibiting coke formation on the surface and/or coils of a pyrolysis furnace. The sulfur oil used in the process of the aforementioned PCT application is a low value product obtained from LPG Mercaptan oxidation units and comprises relatively high concentration of sodium (around 1 ppm). The presence of relatively high level of sodium in the sulfur oil can be detrimental to the reactions wherein the sulfur oil is used.
In the thermal cracking process when di-sulfide oil (sulfur oil) is used as an anti-coking agent, the higher amount of sodium i.e. (= 1ppm) forms sodium oxide and deposits on the surface of the heater tube as a passive layer which inhibits heat transfer and results in coke formation on heater tube. In the hydrothermal reactor, the high amount of sodium present in the di-sulfide oil reacts with the hydrothermal cracking catalyst and forms sodium aluminate layer on catalyst active sites. Alternatively, the sodium reacts with active metals present in the catalyst composition and forms alloy which eventually leads to reduced catalytic activity.
Therefore, in spite of being established as an excellent economical alternative to the conventionally known anti-coking agents and sulfiding agents, the presence of sodium at around 1 ppm level in the di-sulfide oil prevents its further use.
Therefore, there is felt a need to provide a process for the removal of sodium from di-sulfide oil (sulfur oil) produced as a waste or as a by-product stream during the LPG desulfurization process in order to provide an alternative to the existing sulfur containing compounds which is economical and process benign for a number of applications.

OBJECTS:
Some of the objects of the present invention are described herein below:
It is an object of the present invention to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
Another object of the present disclosure is to provide a process for obtaining di-sulfide oil (sulfur oil) having sodium level below 0.1 ppm wherein the di-sulfide oil is obtained as a waste or as a by-product stream from the LPG desulfurization process.
Still another object of the present disclosure is to provide a process for obtaining di-sulfide oil having sodium level below 0.1 ppm wherein the process is very simple, efficient, and economical.
Yet another object of the present disclosure is to provide a useful and economical alternative to the existing anti-coking additives, and sulfiding agents which are used in a number of processes including, but not limited to, hydro-treating, hydro-processing and the like.
Other objects and advantages of the present invention will be more apparent from the following description which is not intended to limit the scope of the present invention.

SUMMARY:
In one aspect the present disclosure provides a process for obtaining di-sulfide oil having sodium level below 0.1 ppm, said process comprising passing a stream comprising di-sulfide oil having sodium level of 1 ppm through an alumina bed packed in a column, at a liquid hourly space velocity (LHSV) ranging from 0.5 to 5.0 hr-1 and at a pre-determined temperature to obtain a treated stream comprising di-sulfide oil having sodium level below 0.1 ppm.
The liquid hourly space velocity (LHSV) ranges from 0.5 to 2 hr-1.
In one embodiment, the liquid hourly space velocity (LHSV) ranges from 1.0 to 1.5 hr-1.
The pre-determined temperature can vary from 10 to 40 oC.
In one embodiment, the pre-determined temperature varies from 20 to 30 oC.
The stream comprising the di-sulfide oil having sodium level of 1 ppm is a waste or a by-product stream collected from LPG desulfurization units.
The treated stream comprising di-sulfide oil has sodium level below 0.05 ppm.
In one embodiment, the treated stream comprising di-sulfide oil has sodium level below 0.02 ppm.
In another embodiment, the treated stream comprising di-sulfide oil has sodium level 0.01 ppm.
Typically, the di-sulfide oil is an organic di-sulfide comprising at least one alkyl sulfide selected from the group consisting of dimethyldisulfide, ethylmethyl disulfide and diethyl disulfide.
Typically, the alumina is characterized by the following properties: average particle size ranging from 0.3 to 0.7mm; pore volume ranging from 44.1 to 71.9 cm3/100g; surface area ranging from 195 to 331 m2/g; and density ranging from 543 to 829 kg/m3.

DETAILED DESCRIPTION:
The disadvantages allied with the use of expensive sulfur containing compounds such as dialkyl disulfides, dialkyl sulfides, and di-sulfide oil which comprise relatively higher concentration of sodium are advantageously alleviated in the present disclosure. As described earlier, the stream comprising di-sulfide oil, obtained as a waste or as a by-product stream during the LPG desulfurization process, comprises a relatively high concentration of sodium which makes it unacceptable for a number of applications such as its use as an anti-coking agent in thermo-cracking processes. The present disclosure therefore provides a process for the removal of sodium from di-sulfide oil, obtained as a waste or a by-product stream from LPG desulfurization process, wherein the concentration of sodium level in the di-sulfide oil is reduced to an amount which is much lower than the acceptable range i.e. 1 ppm, thereby making it useful for a number of applications.
In one aspect, the present disclosure provides a process for obtaining di-sulfide oil having sodium level below 0.1 ppm, said process comprising the steps of collecting a stream comprising di-sulfide oil having sodium level of 1 ppm from LPG desulfurization units and passing the stream through an adsorbent bed under pre-determined operating conditions of volume, time and temperature to obtain a treated stream that comprises di-sulfide oil having sodium level below 0.1 ppm.
The stream collected from the LPG desulfurization unit in accordance with the process of the present disclosure is a waste or a by-product stream.
The adsorbent used in the process of the present disclosure is an inorganic oxide based adsorbent. Example of inorganic oxide based adsorbent suitable for the process of the present disclosure includes alumina. The inventors of the present disclosure have used a number of alumina which differs in their characteristic attributes such as density, pore volume, surface area and the like in order to optimize the process of the present disclosure. The alumina which is useful for the purpose of the present disclosure is an activated alumina with high adsorption capacity owing to its specific surface area and tailored pore size distribution.
The alumina used in the process of the present disclosure is characterized by the following properties: average particle size ranging from 0.3 to 0.7mm; pore volume ranging from 44.1 to 71.9 cm3/100g; surface area ranging from 195 to 331 m2/g; and density ranging from 543 to 829 kg/m3. Further, the alumina used in the process of the present disclosure may be of different shape such as spheres, extrudates, granules and rings.
The alumina adsorbent in accordance with the process of the present disclosure is packed in a glass column fitted with a flow control stop cork. The stream comprising the di-sulfide oil is stored in a separating funnel provided at the top of the glass column. The stream is then passed though the column packed with the alumina adsorbent at a pre-determined liquid hourly space velocity and at a pre-determined temperature. The liquid hourly space velocity (LHSV) typically ranges from 0.5 to 5 hr-1. In accordance with one of the embodiments of the present disclosure, the liquid hourly space velocity ranges from 0.5 to 2 hr -1. In accordance with another embodiment, the liquid hourly space velocity (LHSV) ranges from 1.0 to 1.5 hr-1.The liquid hourly space velocity of the stream passing through the column packed with the alumina adsorbent is controlled though the column and the separating funnel stoppers. The pre-determined temperature typically ranges from 10 to 40 oC. In accordance with one of the embodiments of the present disclosure, the temperature ranges from 20 to 30 oC.
The stream passing though the column packed with the alumina adsorbent is collected at every 2 hour interval (hereinafter referred to as a treated stream) and subjected to an atomic absorption spectroscopy (AAS) and inductively coupled plasma mass spectroscopy (ICPMS) analysis to measure the sodium level. The sodium level of the waste or the by-product stream as collected from LPG desulfurization units is also measured by AAS and it is found to be 1 ppm.
The amount of sodium in the treated stream is found to be typically below 0.1 ppm. In accordance with one of the embodiments of the present disclosure, the amount of the sodium in the treated stream is below 0.05 ppm, preferably below 0.02 ppm, more preferably 0.01 ppm.
The di-sulfide oil in accordance with present disclosure comprises at least one C2-C4 containing alkyl disulfides selected from the group consisting of dimethyl disulfide, ethyl methyl disulfide, diethyl disulfide and the like.
The alumina based adsorbent used in the process of the present disclosure demonstrates excellent adsorption efficiency for the sodium metal present in the di-sulfide oil. The sodium removal efficiency of the alumina adsorbent typically ranges from 98.7 to 99.7 %. Further, the alumina based adsorbent is capable of treating the di-sulfide oil which is at least 200 times the volume of alumina used.
The efficiency of the treated stream containing di-sulfide oil having sodium level below 0.1 ppm is evaluated in a number of applications that include, but are not limited to, its use as an anti-coking additive in the thermal cracking process, as a sulfiding agent for the pre-sulfidization of catalysts used in the hydro-treating and hydro-cracking process, and in the hydrogenation of non-edible vegetable oils to produce bio-fuels.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
Example-1:
30 gms (~48 ml) of alumina (A1) was poured into a glass column (45 cm height and 3.2 cm diameter) with flow control stop cork. The alumina having the following characteristic attributes was used: average particle size: 0.5 mm; density: 629 kg/m3; pore volume: 68.9 cm3/100g; and surface area: 195 m2/g. A stream comprising di-sulfide oil (sulfur oil), produced as a waste or as a by-product stream from mercaptan oxidation units of a refining complex was collected and stored in a 1 liter separating funnel at the top of the column (refer to Table-1 for the properties of the di-sulfide oil collected as a waste stream from the LPG desulfurization process). The stream was then passed though the column packed with alumina (A1) at ambient temperature (25 oC) with liquid hourly space velocity (LHSV) of 1.25 h-1. LHSV was controlled through the funnel and column stoppers. The stream after passing though the alumina bed (referred to as a treated stream) was collected at every 2 hours interval and subjected to AAS (atomic absorption spectroscopy) and inductively coupled plasma mass spectroscopy (ICPMS) for the measurement of Na level. The amount of Na in the treated sample was found to be 0.01 ppm.
Table-1: Characteristic properties of the di-sulfide oil (sulfur oil) collected from mercaptan oxidation units of a refining complex
Sl. No Attributes Unit of measurement Value
1 Appearance - Clear with nil particulates
2 Total Sulphur wt % 60.0 typical
3 Critical temperature Deg C 351
4 Critical pressure , bars 47.8
5 Boiling range ?C 110-180
6 Density (20deg C) g/cc 1.03
7 Viscosity (20deg C) cps 0 .597
8 Vapor pressure (20deg C) mbar 13.6
9 Surface tension (20deg C) dynes/cm 33.6
10 Specific heat (25deg C) KJ/Kg-K 1.521
11 Na ppm w 1.0 max
12 Co ppm 0.25 max
13 Cu ppm 0.10 max
14 Fe ppm 0.20 max

Example-2:
In this example, the treatment of the di-sulfide oil collected from mercaptan oxidation units of a refining complex was carried out in the same manner as described in example-1, except an alumina adsorbent having higher density, and lower pore volume and lower surface area (A2) as compared to the alumina (A1) was used. Characteristic attributes of the alumina adsorbent (A2) are provided in Table-2. The amount of Na in the treated stream was analyzed similar to example-1, and was found to be 0.04 ppm.

Example-3:
In this example, the treatment of the di-sulfide oil collected from mercaptan oxidation units of a refining complex was carried out in the same manner as described in example-1, except an alumina adsorbent (A3) of lower density, and higher pore volume and higher surface area as compared to the alumina (A1) was used. Characteristic features of the alumina adsorbent (A3) are provided in Table-2. The amount of Na in the treated stream by analyzed similar to example-1, and was found to be 0.01 ppm. Further, the sodium removal efficiency of the alumina adsorbent A1, A2 and A3 is also provided in Table-3.
Table-2: Characteristic features of the alumina used:
Typical Characteristics Unit of measurement Alumina adsorbent
A3 Alumina adsorbent
A2 Alumina adsorbent
A1
Al2O3 wt% 93.5 min. 93.5 min. 93.5 min.
Na2O ppm (w) 3200 max. 3200 max. 3200 max.
Shape - extrudates beads beads
Average particle size mm 0.5 0.5 0.5
Density DRT kg/m3 543 829 629
Total porous volume VPT cm3/100 g 71.9 44.1 68.9
Mechanical strength EGG daN 1.4/mm 12.1 5.3
Surface area BET m2/g 320 331 195
Loss on ignition (300 -1000°C) wt% 5 max. 5 max. 5 max.
Static adsorption (at 60% RH) wt% 21 21 21
Table-3: Sodium removal efficiency of various adsorbents:
Sr. No Di-sulfide oil Adsorbent
Al2O3 Na in ppm Removal Efficiency
1. Di-sulfide oil (untreated)
None 3 -
2. Treated di-sulfide oil A2 0.04 98.7%
3. Treated di-sulfide oil A1 0.01 99.7%
4. Treated di-sulfide oil A3 0.01 99.7%

Example-4:
In this example, the treatment of the di-sulfide oil was carried out in the same manner as described in example-1, except the LHSV value of 2 hr-1. The amount of Na in the treated di-sulfide oil was analyzed similar to example-1, and was found to be 0.04 ppm.
Example-5:
In this example, the treatment of the di-sulfide oil was carried out in the same manner as described in example-1, except the LHSV value of 5 hr-1. The amount of Na in the treated di-sulfide oil was analyzed similar to example-1, and was found to be 0.1 ppm.
Example-6:
In this example, the treatment of the di-sulfide oil collected from a LPG desulfurization was carried out in the same manner as described in example-1, except the temperature which was maintained at 30 oC. The amount of Na in the treated di-sulfide oil was analyzed similar to the example-1, and was found to be 0.01 ppm.

TECHNICAL ADVANCEMENTS:
The present disclosure related to a process for removal of Na from di-sulfide oil, has several technical advancements, including but not limited to the realization of:
1. A very simple and efficient process for the removal of sodium from di-sulfide oil, a waste product obtained from LPG desulfurization process,
2. An economic alternative to the existing anti-coking agent, for example di-methyl disulfide (DMDS), by providing di-sulfide oil having sodium level below 0.1 ppm which can be used very efficiently as an anti-coking agent in the thermal cracking of hydrocarbons with practically no change in the cracking product composition and/or energy requirement,
3. An economic alternative to the existing sulfiding agents such as di-methyldisulfide (DMDS) used in the hydro-processing of non-edible vegetable oils to produce bio-jet or bio-diesel, and
4. An economic alternative to the existing pre-sulfiding agent used in the hydrotreaters and hydrocrackers for the pre-sulfidization of the catalyst.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the invention, unless there is a statement in the specification specific to the contrary.

The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.