DESC:FIELD
The present disclosure relates to a process for reducing carbon disulphide content of a hydrocarbon feed.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.
Hydrotreating catalyst: The hydrotreating catalyst is the catalyst used for hydrogenating or reducing heavy hydrocarbons to light hydrocarbons.
BACKGROUND
Naphtha is an important intermediate stream obtained through distillation of crude oil or thermal and/or catalytic cracking of hydrocarbon streams. Broadly, naphtha can be split into light naphtha and heavy naphtha. Heavier naphtha is used in the catalytic reforming process to produce high-octane gasoline, whereas, the lighter naphtha becomes a component of finished gasoline or invariably goes to the petrochemical naphtha pool, which is the predominant feedstock for steam crackers.
Carbon disulphide (CS2) in the petrochemical naphtha is a highly undesired contaminant for downstream processing units and its final products. High concentration of CS2 affects many downstream refinery processes, such as cracking of naphtha, hydrogenation processes, and the like. High content of CS2 in the hydrocarbon feed is responsible for permanent poisoning of catalysts used in different hydrotreating processes. Thus, removal of CS2 from naphtha is necessary to meet the stringent specifications of CS2 concentration in the hydrocarbon feed.
Hydrodesulphurization is one of the methods for reducing the amount of CS2 from the hydrocarbon feed. Hydrodesulphurization of naphtha is aimed to achieve removal/reduction of sulphur and nitrogen contaminants to a desired level. However, it is difficult to reduce CS2 from the hydrocarbon feed in the presence of other sulphur compounds like dimethyl sulphide, C4H10S, C2H6S2, and C4H4S.
Therefore, there is felt a need to provide a process for selectively reducing the carbon disulphide content of the hydrocarbon feed.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to provide a simple and efficient process for reducing the carbon disulphide content of a hydrocarbon feed.
Another object of the present disclosure is to provide a process for selectively reducing the carbon disulphide content of the hydrocarbon feed.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure relates to a process for reducing the carbon disulphide content of a hydrocarbon feed. The process comprises mixing a hydrocarbon feed having carbon disulphide content >2 ppm and hydrogen at a temperature in the range of 80 °C to 100 °C to obtain a gas –liquid mixture. The volume/volume ratio of hydrogen to the hydrocarbon feed in the mixture is in the range of 5:1 to 10:1. The so obtained mixture is hydrotreated in the presence of a catalyst in a reactor at a temperature in the range of 80 oC to 150 oC at a pressure in the range of 3 bar to 15 bar. The process is carried out at a liquid hourly space velocity in the range of 3 hour-1 to 10 hour-1 to obtain hydrocarbon stream having carbon disulphide < 2ppm.
More specifically, the process for reducing the carbon disulphide content of a hydrocarbon feed of the present disclosure comprises mixing a predetermined amount of the hydrocarbon feed with hydrogen in a feed mixer to obtain a first gas-liquid mixture. The first gas-liquid mixture is then passed to a pre-heater where it is heated at a temperature in the range of 80 °C to 100 °C to obtain a second gas-liquid mixture. The so formed second gas-liquid mixture is then fed to a reactor containing a catalyst for hydrotreating at a temperature in the range of 80 °C to 150 °C at a pressure in the range of 3 bar to 15 bar at a liquid hourly space velocity in the range of 3 hour-1 to 10 hour-1 to obtain a treated mixture. The treated mixture is cooled to obtain a third gas-liquid mixture. The liquid is separated from the third gas-liquid mixture to obtain hydrocarbon having carbon disulphide content (CS2 content) < 2 ppm.
In one embodiment of the present disclosure, the process comprises a pre-step of sulphidation of said hydrotreating catalyst.
On contacting the hydrocarbon feed with hydrotreating catalyst under optimized reaction conditions, carbon disulphide is reduced to methane and hydrogen sulphide. The hydrocarbon feed of the present disclosure can be petroleum naphtha. The hydrotreating catalyst can be cobalt and molybdenum impregnated on Al2O3 substrate.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING:
A process for reducing the carbon disulphide content of a hydrocarbon feed will now be described with the help of the accompanying drawing in which
Figure 1 illustrates a hydrotreating system for carrying out the process for reducing the carbon disulphide content from the hydrocarbon feed.
DETAILED DESCRIPTION
Carbon disulphide (CS2) content in petrochemical naphtha is highly undesired, as CS2 acts as a contaminant for downstream processing units and its final products. High concentration of CS2 affects many downstream refinery processes, such as cracking of naphtha, and hydrogenation process.
Therefore, the present disclosure envisages a process for reducing the carbon disulphide content of a hydrocarbon stream to below 2 ppm. The process comprises contacting a mixture of a hydrocarbon feed and hydrogen at a temperature ion the range of 80 oC to 100 oC to obtain gas-liquid mixture and hydrotreating the mixture in the presence of a catalyst in a reactor at a temperature in the range of 80 °C to 150 °C and at a pressure in the range of 3 bar to 15 bar to obtain a hydrocarbon stream having carbon disulphide < 2 ppm..
The process of the present disclosure is carried out at a liquid hourly space velocity of the hydrocarbon feed in the range of 3 hour-1 to 10 hour-1, and the volume/volume ratio of hydrogen to the hydrocarbon feed is in the range of 5:1 to 10:1.
Figure 1 illustrates a schematic diagram of a system for reducing the carbon disulphide content of a hydrocarbon feed in accordance with the embodiments of the present disclosure. The system 100 comprises a pre-mixer 102, that is configured to receive hydrogen gas from a first inlet 101a and a hydrocarbon feed from a second inlet 101b to obtain an intensely mixed mixture. A pre-heater 103 is configured to heat the intensely mixed mixture of hydrogen gas and the hydrocarbon feed received from the pre-mixer 102. A reactor 104 is configured to receive the heated gas-liquid mixture. The reactor 104 contains a catalyst that aids in the conversion of the carbon disulphide content in the hydrocarbon feed into methane and hydrogen sulfide a condenser or chiller 105 is disposed downstream of and in fluid communication with the reactor 104. The condenser 105 is configured to receive the mixture of hydrocarbon feed containing methane and hydrogen sulfide. Further, the hydrocarbon feed (gas), methane and hydrogen sulfide mixture are fed to a high pressure gas-liquid separator 106 that is in fluid communication with the condenser 105, wherein the methane and hydrogen sulfide are at least partly separated from the hydrocarbon feed. Thereafter, the hydrocarbon feed is fed to a low pressure gas-liquid separator 107 that is in fluid communication with the high pressure gas-liquid separator 106, wherein the hydrocarbon stream with reduced carbon disulphide content is obtained.
The process for reducing the carbon disulphide content of the hydrocarbon feed using the system 100 is described herein below.
A predetermined amount of hydrogen and a predetermined amount of hydrocarbon feed are introduced into the pre-mixer 102 via the inlets 101a and 101b respectively, wherein the hydrocarbon feed and hydrogen are intensely mixed to obtain a first gas-liquid mixture. The first gas-liquid mixture heated by the preheater 103, wherein the first gas-liquid mixture is heated to a temperature in the range of 80 °C to 100 °C to obtain a second gas-liquid mixture. The second gas-liquid mixture is fed to the reactor 104 containing the hydrotreating catalyst at a temperature in the range of 80 °C to 150 °C and at a pressure in the range of 3 bar to 15 bar to obtain a treated mixture. The second gas-liquid mixture, on coming in contact with the hydrotreating catalyst at the above mentioned temperature and pressure conditions, results in the reduction of carbon disulphide present in the second gas-liquid mixture, is being converted to methane and hydrogen sulphide.
Further, the treated mixture is then fed to the condenser 105, wherein the hydrocarbon feed is condensed to obtain a third gas-liquid mixture comprising liquid hydrocarbon stream with reduced carbon disulphide content. The liquid is separated from the third gas-liquid mixture in the high pressure gas-liquid separator 106 and thereafter in the low pressure gas-liquid separator 107 to obtain treated hydrocarbon stream with reduced carbon disulphide content.
The hydrocarbon comprises carbon disulphide in the range of 1.6 to 0.15.
The catalyst used in the hydrotreating process of the present disclosure can be a cobalt-molybdenum. More specifically, the catalyst can be cobalt and molybdenum impregnated on Al2O3 substrate.
Further, the process involves a pre-step of sulphidation of the hydrotreating catalyst before contacting the hydrocarbon feed containing the carbon disulphide content. The step of sulphidation of the hydrotreating catalyst can be achieved by passing H2S gas through a catalyst bed placed in the reactor. The sulphidation of the hydrotreating catalyst is helpful in reducing the carbon disulphide to methane and hydrogen sulphide.
The hydrocarbon feed can be naphtha and the carbon disulphide content can be in the range of 15 to 50 ppm.
An advantage of the process of the present disclosure is that it facilitates selective reduction of the carbon disulphide content of the hydrocarbon feed in the presence of other sulphur compounds.
The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and are not to be construed for limiting the scope of the disclosure. The following experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.
Experimental Details:
Experiments 1-7: Hydrotreating process
The experiment 1 was performed using the system 100 as described in the description of the present disclosure.
Hydrogen and naphtha were introduced in the pre-mixer 102 via the inlet lines 101a and 101b respectively, with the volume ratio of hydrogen to naphtha being 8:1, wherein the naphtha and hydrogen were intensely mixed to obtain a first gas-liquid mixture. The amount of carbon disulphide present in the naphtha before entering the pre-mixer 102 was 35 ppm and total sulphur (TS) content was 341 ppm. A static mixer was used as a pre-mixer 102. The gas-liquid mixture was then introduced into the pre-heater 103, which was maintained at 100 °C to obtain a second gas-liquid mixture. Thereafter, the second gas-liquid mixture from the pre-heater 103 was introduced into a reactor 104 that was maintained at 150 °C, and a pressure of 15 bar. The reactor contained a hydrotreating catalyst, which on contact with the naphtha reduces carbon disulphide of naphtha to methane and hydrogen sulphide to obtain treated naphtha. Next, the treated naphtha was fed to a condenser maintained at a temperature in the range of 5 °C to 6 °C to obtain the third gas-liquid mixture. The gaseous naphtha d on passing through the condenser got converted to liquid hydrocarbon feed. The third gas-liquid mixture was fed to the high pressure separator and subsequently to a low pressure separator, where the liquefied hydrocarbon feed was separated from the gaseous mixture to obtain a treated feed having reduced carbon disulphide content.
Further, experiments 2-4 were performed to optimize the process variables mentioned in the experiment 1. The pressure was maintained at 8 bar, gas (hydrogen) to oil (naphtha) volume ratio and space velocity constant were maintained at 8:1and 5 hour-1 respectively. Further, the hydrogen to hydrocarbon feed ratio was increased to 16 ml/ml keeping the pressure and space velocity constant. In the subsequent attempt the pressure inside the reactor was set at 5 bar keeping all other variables constant. In this set of experiments all the treated feeds were found to have carbon disulphide reduced to more than 97%, while the total sulphur (TS) removal also was found to be not more than 12%. Thus, the presently disclosed process gives highly selective carbon disulphide reduction while marginally reducing other sulphur compounds in the hydrocarbon feed.
Experiments 5-7 were performed by varying LHSV. Experiment 5 was performed at LHSV 5 hour-1, experiment 6 at 7.5 hour-1 and experiment 7 at 10 hour-1, keeping the pressure in the reactor constant at 5 bar and the temperature inside the reactor at 123 °C, and hydrogen to naphtha ratio of 8:1.
The process parameters and results of experiments 1-7 are presented in Table 1.
For the analysis of treated mixtures of experiment 1 to 7, SCD (Sulphur Chemiluminescence Detector) was used.
Table 1: The reaction conditions and result of the process of reducing carbon disulphide content from naphtha.
Exp. Temp.
(°C) Pressure,
(bar) G/O LHSV,
hour-1 CS2 in feed (ppm) CS2 in treated stream (ppm) TS in Feed (ppm) TS in treated Feed (ppm)
1 150 15 8:1 5.0 35 0.3 341 315
2 123 8.0 8:1 5.0 35 1.2 341 313
3 123 8.0 16:1 5.0 35 1.2 341 299
4 123 5.0 8:1 5.0 35 0.4 341 301
5 123 5.0 8:1 5.0 18 0.4 351 318
6 123 5.0 8:1 7.5 18 0.6 351 330
7 123 5.0 8:1 10 18 1.6 351 348
G/O: gas to oil ratio (gas is hydrogen and oil is naphtha), TS: total sulphur
From Table 1, it is evident that CS2 present in the feed in experiment 1 was 35 ppm, which decreased to 0.3 ppm. The reduction of CS2 achieved is >99% at given reaction conditions. Whereas, other sulphur compound removal provided under heading “total sulphur in feed” did not change much. Therefore, it is evident that the process of the present disclosure is helpful in reducing the carbon disulphide content from naphtha even in the presence of other sulphur compounds.
In all subsequent experiments (2-4), it is found that carbon disulphide is reduced by more than 97%, while the total sulphur (TS) reduction is not more than 12%. Thus, the present disclosure provides a highly selective carbon disulphide reduction process while marginally reducing other sulphur compounds.
Further, the results of experiments 5-7 corroborate the selective removal of carbon disulphide from naphtha feed as depicted in the earlier set of experiments. More than 96% CS2 reduction is achieved, while the total sulphur removal is found to be less than 10%.

Experiments 8- 14: Hydrotreating process:
Experiments 8-14 were performed by keeping the temperature constant inside the reactor at 120 °C. The pressure in the reactor was varied from 5 bar to 15 bar, whereas gas (hydrogen) to oil (naphtha) volume ratio was changed as 5:1, and 8:1. The results of the experiments 8-14 are summarized in Table 2.
Table 2: Reaction parameters and results of experiment 8-14
Exp. Temp.
(°C) Pressure,
(bar) G/O LHSV,
hour-1 CS2 in feed (ppm) CS2 in treated stream (ppm) TS in Feed (ppm) TS in treated Feed (ppm)
8 120 15.0 8:1 5.0 18.4 0.16 236 224
9 120 15.0 8:1 8.0 18.4 0.25 236 206
10 120 15.0 8:1 10.0 18.4 0.44 236 227
11 120 15.0 5:1 10.0 18.4 0.30 236 217
12 120 15.0 5:1 8.0 18.4 0.32 236 210
13 120 5.0 8:1 5.0 18.4 0.15 236 226
14 120 5.0 8:1 5.0 18.4 0.15 236 220
G/O: gas to oil ratio (gas is hydrogen and oil is naphtha), TS: total sulphur

The hydrotreating reaction, when carried out at temperature 120 °C, carbon disulphide reduction was found to be more than 96%, with minimal other sulphur species being removed.
Therefore, it can be concluded that, the process of the present disclosure, is helpful in reducing carbon disulphide content from hydrocarbon feed selectively, in the presence of other sulphur compounds even at milder reaction conditions.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process that
- is simple and efficient; and
- facilitates in the removal of carbon disulphide content from the hydrocarbon feed up to a desired level of less than 2 ppm.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results. While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Variations or modifications to the formulation of this invention, within the scope of the invention, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this invention.
The numerical values given for various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the invention unless there is a statement in the specification to the contrary.
While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.

,CLAIMS:WE CLAIM
1. A process for obtaining a hydrocarbon stream having carbon disulphide < 2 ppm, said process comprising:
• mixing a hydrocarbon feed having carbon disulphide content > 2 ppm and hydrogen at a temperature in the range of 80 oC to 100 oC to obtain a gas-liquid mixture, wherein the volume/volume ratio of hydrogen to said hydrocarbon feed is in the range of 5:1 to 10:1;
• hydrotreating said mixture in the presence of a catalyst in a reactor at a temperature in the range of 80 to 150 °C and at a pressure in the range of 3 to 15 bar; and
• carrying out said step of hydrotreatment at a liquid hourly space velocity in the range of 3 hour-1 to 10 hour-1 to obtain a hydrocarbon stream having carbon disulphide < 2 ppm.

2. The process as claimed in claim 1 comprising the following steps:
a. mixing said hydrocarbon feed with hydrogen to obtain a first gas-liquid mixture;
b. heating said first gas-liquid mixture at a temperature in the range of 80 to 100 °C to obtain a second gas-liquid mixture;
c. hydrotreating said second gas-liquid mixture in the presence of a catalyst at a temperature in the range of 80 to 150 °C, at said pressure in the range of 3 to 15 bar, and at said liquid hourly space velocity in the range of 3 hour-1 to 10 hour-1 to obtain a treated mixture,
d. cooling said treated mixture to obtain a third gas-liquid mixture; and
e. separating the liquid from said third gas-liquid mixture to obtain the hydrocarbon stream having carbon disulphide content < 2 ppm.

3. The process as claimed in claim 1 comprising the following steps:
a. mixing said hydrocarbon feed with hydrogen in the volume/volume ratio of 1:8 to obtain a first gas-liquid mixture;
b. heating said first gas-liquid mixture at 100 °C to obtain a second gas-liquid mixture;
c. hydrotreating said second gas-liquid mixture in the presence of a catalyst at a temperature of 150 °C, at a pressure of 15 bar, at a liquid hourly space velocity of 5 hour-1, to obtain a treated mixture;
d. cooling said treated mixture to obtain a third gas-liquid mixture; and
e. separating the liquid from said third gas-liquid mixture to obtain hydrocarbon stream having carbon disulphide content < 2 ppm.

4. The process as claimed in any one of the claims 1, 2, and 3 further comprises sulphidation of said hydrotreating catalyst.

5. The process as claimed in any one of claims 1, 2, and 3 wherein said hydrocarbon feed is naphtha comprising carbon disulphide in the range of 15 to 50 ppm.

6. The process as claimed in any one of claims 1, 2, and 3 wherein said hydrotreating catalyst comprises cobalt and molybdenum impregnated on Al2O3 substrate.

7. The process as claimed in any one of claims 1, 2, and 3 wherein said hydrocarbon stream comprises carbon disulphide in the range of 1.6 to 0.15 ppm.