DESC:FIELD
The present disclosure relates to a process for reducing aromatic hydrocarbons and sulfur from a hydrocarbon feedstream.
BACKGROUND
Petroleum fractions obtained from crude distillation units, typically, comprise a mixture of aromatic hydrocarbons and undesirable elements, such as sulfur which limit their industrial applications. For instance, the content of aromatic hydrocarbons in naphtha streams should be less than 5 wt%, for use in petrochemical industries as a feedstock for producing olefins. Low aromatic hydrocarbons content in naphtha, i.e. less than 10 wt%, is required to increase hydrogen yields in fertilizer industries. Further, hydrocarbons such as kerosene, aviation turbine, and the like have to meet final product specifications like smoke point and aromatic hydrocarbons content, since the performance of the hydrocarbons depend on these specifications. Furthermore, petroleum fractions having a very low aromatic content, i.e. less than 100 ppm, and very low sulfur content, i.e., less than 1 ppm, can be used as solvents in disparate applications.
Similarly, it is recommended that the sulfur content in the hydrocarbons should be minimum, so as to reduce sulfur dioxide (SO2) emissions that result from combusting the hydrocarbons in internal combustion engines, power plants, and furnaces.
Various conventional processes, for example hydrotreating, solvent extraction adsorption, and hydro-desulfurization are used for reducing the amount of aromatic hydrocarbons and sulfur from the hydrocarbons. However, these processes, when used as a stand-alone process, cannot reduce the amount of aromatic hydrocarbons and sulfur to a desired level, i.e., less than 100 ppm and less than 1 ppm respectively.
Moreover, these processes are capital intensive, because these processes harness:
• excess amounts of solvents; and
• a significant amount of hydrogen.
There is, therefore, felt a need for a process to reduce the amount of aromatic hydrocarbons and sulfur from hydrocarbons or petroleum fractions and obviate the drawbacks associated with the conventional processes.
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 process for reducing the amount of aromatic hydrocarbons from hydrocarbons or petroleum fractions.
Another object of the present disclosure is to provide a process for reducing the amount of sulfur from hydrocarbons or petroleum fractions.
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 envisages a process for reducing aromatic hydrocarbons and sulfur contained in a hydrocarbon feedstream. The hydrocarbon feedstream is hydrotreated, in the presence of hydrogen having a pre-determined liquid hourly space velocity and a catalyst, and at a first pre-determined temperature, at a first pre-determined pressure and for a first pre-determined time period, to obtain a hydrotreated hydrocarbon stream comprising a gaseous phase and a liquid phase. The liquid phase and the gaseous phase are separated from the hydrotreated hydrocarbon stream to obtain a separated liquid phase. The separated liquid phase is then contacted with an adsorbent, at a second pre-determined temperature, at a second pre-determined pressure and for a second pre-determined time period, to obtain a hydrocarbon stream with reduced aromatic hydrocarbons and sulfur.
In accordance with the present disclosure, the aromatic hydrocarbons and sulfur in the hydrocarbon stream can be less than 100 ppm and 1 ppm respectively.
In the step of adsorption, the ratio of the separated liquid phase and the adsorbent can be in the range of 5:1 to 50:1.
In the step of hydrotreatment, the ratio of hydrogen to the hydrocarbon feedstream can be in the range of 205 Nm3/ m3 to 405 Nm3/ m3.
The adsorbent can be at least one selected from the group consisting of molecular sieve zeolite 3A, molecular sieve zeolite 4A, molecular sieve zeolite 5A, molecular sieve zeolite 13X and activated carbon.
The catalyst used can be a bimetallic catalyst.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
A process for reducing aromatic hydrocarbons and sulfur contained in a hydrocarbon feedstream will now be described with the help of the accompanying drawing, in which:
Figure 1 illustrates a flow chart depicting the flow of a hydrocarbon stream in accordance with the process of the present disclosure.
DETAILED DESCRIPTION
As discussed herein above, conventional processes, such as hydrotreating, solvent extraction adsorption, and hydro-desulfurization, when used as a stand-alone process, cannot reduce the amount of aromatic hydrocarbons and sulfur to a desired level, i.e., less than 100 ppm and less than 1 ppm respectively. Moreover, excess amounts of solvents and a significant amount of hydrogen are utilized by the conventional processes, thereby increasing the operating cost of the conventional processes.
The present disclosure, therefore, provides a process for reducing the amount of aromatic hydrocarbons and sulfur contained in a hydrocarbon feedstream and obviating the drawbacks associated with the conventional processes.
The process of the present disclosure is described in conjunction with a flow chart depicted in Figure 1. The hydrocarbon feedstream (2) is hydrotreated in a hydrotreatment unit (100), at a first pre-determined temperature, at a first pre-determined pressure and for a first pre-determined period, in the presence of hydrogen having a pre-determined liquid hourly space velocity (LHSV) and a catalyst, to obtain a hydrotreated hydrocarbon stream (4) comprising a gaseous phase (6) and a liquid phase (8). The hydrotreated hydrocarbon stream (4) is introduced into a gas-liquid separation unit (200) to separate and obtain the gaseous phase (6) from an operative upper portion of the gas-liquid separation unit (200) and the liquid phase (8) from an operative lower portion of the gas-liquid separation unit (200). The separated liquid phase (8) is then contacted with an adsorbent in an adsorption unit (300), at a second pre-determined temperature, at a second pre-determined pressure and for a second pre-determined period, to adsorb a portion of the aromatic hydrocarbons and sulfur contained in the liquid phase and obtain a hydrocarbon stream with reduced aromatic hydrocarbons and sulfur. A liquid stream (10) containing the reduced amount of the aromatic hydrocarbons and sulfur exits the adsorption unit (300).
In accordance with the present disclosure, the hydrocarbon feedstream is treated by using two different processes, viz. hydrotreatment and adsorption, because the hydrotreating process is capable of reducing the aromatic hydrocarbons and sulfur to a certain extent, i.e., to a point till equilibrium is achieved. Beyond the equilibrium point, it is not possible to further reduce the amount of the aromatic hydrocarbons and sulfur contained in the hydrocarbon stream, using the hydrotreating process. Therefore, the hydrocarbon stream is further treated using the adsorption process, wherein the amount of the aromatic hydrocarbons and sulfur contained in the hydrocarbon stream is further reduced to a desired value.
Therefore, the process of the present disclosure is an integrated process of hydrotreatment and adsorption.
The hydrocarbon feedstream (2) can be at least one of naphtha, kerosene, diesel, petrol, jet fuel, and lubricating oil.
In accordance with the present disclosure, the hydrocarbon feedstream (2) hydrotreated in the hydrotreatment unit (100), contains aromatic hydrocarbons and sulfur in an amount in the range of 200000 ppm to 300000 ppm and 3000 ppm to 4000 ppm respectively.
In accordance with the present disclosure, the liquid phase (8) of the hydrotreated hydrocarbon stream (4) contains aromatic hydrocarbons and sulfur in a reduced amount ranging from 10000 ppm to 20000 ppm and less than 5 ppm respectively.
In accordance with the present disclosure, in the adsorption step, aromatic hydrocarbons and sulfur contained in the separated liquid phase (8) can be reduced to a desired value, i.e., to an amount less than 100 ppm and 1 ppm respectively.
In accordance with the present disclosure, the first pre-determined temperature can be in the range of 300ºC to 400ºC, the first pre-determined pressure can be in the range of 60 bar to 100 bar and the first pre-determined time period can be in the range of 1 hour to 4 hour.
In accordance with the present disclosure, the second pre-determined temperature can be in the range of 20ºC to 400ºC, the second pre-determined pressure can be atmospheric pressure and the second pre-determined time period can be in the range of 1 hour to 3 hour.
In accordance with the present disclosure, the LHSV of hydrogen can be in the range of 0.5 h-1 to 3.0 h-1.
In accordance with the present disclosure, the gaseous phase (6) leaving the gas-liquid separation unit (200) can be processed further to separate aromatic hydrocarbons and sulfur therefrom. The aromatic hydrocarbons separated from the gas-liquid separation unit (200) can be used as solvents in varied applications.
The aromatic hydrocarbons include, but are not limited to, benzene, toluene and xylene.
In accordance with the present disclosure, the ratio of the separated liquid phase (8) and the adsorbent, in the step of adsorption, can be in the range of 5:1 to 50:1.
In accordance with the present disclosure, the ratio of hydrogen to the hydrocarbon feedstream (2), in the step of hydrotreatment, can be in the range of 205 Nm3/ m3 to 405 Nm3/ m3.
In accordance with the present disclosure, the adsorbent can be at least one selected from the group consisting of molecular sieve zeolite 3A, molecular sieve zeolite 4A, molecular sieve zeolite 5A, molecular sieve zeolite 13X and activated carbon.
In accordance with the present disclosure, the catalyst used in the hydrotreating process is a bimetallic catalyst which can be one of Co-Mo/Al2O3 and Ni-Mo/Al2O3.
In accordance with one embodiment of the present disclosure, the bimetallic catalyst can be regenerated and reused in the hydrotreating process.
The integrated process of the present disclosure is capable of reducing more than 96% and 99% of the aromatic hydrocarbons and sulfur respectively, contained in the hydrocarbon feedstream (2). Moreover, the operating cost of the integrated process of the present disclosure is less as compared to the stand-alone conventional processes.
The hydrocarbon stream with reduced amount of the aromatic hydrocarbons and sulfur can be used for producing a superior quality of special boiling point solvents.
The process of the present disclosure is associated with an advantage that the combined sequential steps of hydrotreating and adsorption reduce the amount of aromatic hydrocarbons and sulfur contained in the hydrocarbon feedstream to a desired value.
The present disclosure is further described in light of the following experiments, which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following experiment can be scaled up to industrial/commercial scale.
Experiment 1: Process for reducing aromatic hydrocarbons and sulfur contained in kerosene.
[A] Hydro-treatment of kerosene:
Table 1: illustrates the properties of kerosene.
Parameter Value
Initial boiling point/ Final boiling point (IBP/FBP), oC 149.5/247.5
Density, g/cc 0.791
Viscosity at 30 oC, cSt 1.4742
Sulfur, ppm 3400
Flashpoint, oC 46.5
Saturates, wt% 76.6
Total Aromatic Hydrocarbons, ppm 234000
Hydrotreating of kerosene was carried out in the hydrotreatment unit (100) over a Co-Mo/ Al2O3 based catalyst. Before hydrotreating the kerosene, the Co-Mo/ Al2O3 based catalyst was dried and pre-sulfided using dimethyl disulfide (DMDS) having 2.5 wt% of sulfur concentration to enhance the activity of the Co-Mo/ Al2O3 based catalyst. After pre-sulfiding the catalyst, kerosene was hydrotreated in the hydrotreatment unit (100) in the presence of hydrogen and the Co-Mo/ Al2O3 based catalyst for 8 hours. Hydrotreating of kerosene was carried out at different process conditions to identify variation in the amount of aromatic hydrocarbons and sulfur in kerosene.
Different process conditions and its effect on the amount of aromatic hydrocarbons and sulfur in kerosene are provided in Table 2.
Table 2:
Sr.
no Temp
oC Pressure
bar LHSV
h-1 Sulfur
ppm Density
gm/cc Aromatic hydrocarbons
ppm
1 320 80 1 10 0.783 53000
2 330 80 1 6 0.782 28000
3 340 80 1 <5 0.778 8000
4 360 80 0.8 < 5 0.779 11000
5 360 80 0.6 < 5 0.778 10200
From Table 2, it is found that by optimizing the operating conditions of the hydrotreatment unit (100), i.e., at a temperature of 340oC, a pressure of 80 bar and a LHSV of 1 h-1 of hydrogen, the amount of aromatic hydrocarbons and sulfur in kerosene reduced to 8000 ppm and below 5 ppm respectively.
Moreover, from Table 2, it is found that with increase in temperature and decrease in LHSV of hydrogen, the amount of aromatic hydrocarbons in kerosene increases as compared to that found in kerosene at 340oC.
The desired value of the aromatic hydrocarbons and sulfur in kerosene should be less than 100 ppm and 1 ppm respectively. However, it is evident from Table 2 that the hydrotreated kerosene contains 8000 ppm and less than 5 ppm of the aromatic hydrocarbons and sulfur respectively. Therefore, in order to get the desired value, the hydrotreated kerosene is subjected to adsorption.
[B] Subjecting the hydro-treated kerosene to adsorption:
2 litres of hydrotreated kerosene obtained from the step A was taken in a glass vial. 1 gm of molecular sieve zeolite 13 X was used as an adsorbent having 800 m2/g of surface area. The adsorbent was pre-treated by subjecting the adsorbent to 250oC in the presence of nitrogen followed by cooling the adsorbent to 100oC in the presence of nitrogen. The pre-treated adsorbent was transferred to the glass vial and mixed with 20 liters of kerosene. The process of adsorption was carried out at 25oC and for 24 hours. The results obtained during experimentation using a varying ratio of kerosene and adsorbent are tabulated in Table 3.
Table 3
Kerosene to adsorbent ratio wt/wt Aromatic hydrocarbons
ppm Sulfur,
ppm
50 5048 < 1
40 3921 < 1
30 2850 < 1
15 1023 < 1
5 <100 < 1
From Table 3, it is found that on further treating the hydrotreated kerosene by the process of adsorption, which is carried out using an appropriate ratio of kerosene to adsorbent, i.e., 5 (wt/wt) and for a period of 24 hours, it is possible to reduce the aromatic hydrocarbons and sulfur in the hydrotreated kerosene to an amount less than 100 ppm and 1 ppm respectively.

TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process that:
? reduces the amount of aromatic hydrocarbons in the hydrocarbon feedstream; and
? reduces the amount of sulfur in the hydrocarbon feedstream.
The disclosure has been described with reference to the accompanying embodiments which do not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.
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 foregoing description of the specific embodiments so fully revealed 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. ,CLAIMS:1. A process for reducing aromatic hydrocarbons and sulfur contained in a hydrocarbon feedstream, said process comprising the following steps:
a) hydrotreating said hydrocarbon feedstream, in the presence of hydrogen having a pre-determined liquid hourly space velocity and a catalyst, at a first pre-determined temperature, at a first pre-determined pressure and for a first pre-determined time period, to obtain a hydrotreated hydrocarbon stream comprising a gaseous phase and a liquid phase;
b) separating said liquid phase from said hydrotreated hydrocarbon stream to obtain a separated liquid phase; and
c) contacting said separated liquid phase with an adsorbent, at a second pre-determined temperature, at a second pre-determined pressure and for a second pre-determined time period, to obtain a hydrocarbon stream with reduced aromatic hydrocarbons and sulfur, wherein said aromatic hydrocarbons and said sulfur in said hydrocarbon stream is less than 100 ppm and 1 ppm respectively.
2. The process as claimed in claim 1, wherein said:
• first pre-determined temperature is in the range of 300ºC to 400ºC;
• first pre-determined pressure is in the range of 60 bar to 100 bar; and
• first pre-determined time period is in the range of 1 hour to 8 hour.
3. The process as claimed in claim 1 or claim 2, wherein said:
• second pre-determined temperature is in the range of 20ºC to 400ºC;
• second pre-determined pressure is atmospheric pressure; and
• second pre-determined time period is in the range of 1 hour to 4 hour.
4. The process as claimed in claim 1 or claim 2, wherein said pre-determined liquid hourly space velocity of hydrogen is in the range of 0.5 h-1 to 3.0 h-1.
5. The process as claimed in claim 1, wherein in the step of adsorption, the ratio of said separated liquid phase and said adsorbent is in the range of 5:1 to 50:1.
6. The process as claimed in claim 1, wherein said adsorbent is at least one selected from the group consisting of molecular sieve zeolite 3A, molecular sieve zeolite 4A, molecular sieve zeolite 5A, molecular sieve zeolite 13X and activated carbon.
7. The process as claimed in claim 1, wherein in the step of hydrotreatment, the ratio of hydrogen to said hydrocarbon feedstream is in the range of 205 Nm3/ m3 to 405 Nm3/ m3.
8. The process as claimed in claim 1, wherein said catalyst is a bimetallic catalyst.
9. The process as claimed in claim 8, wherein said bimetallic catalyst is one of Co-Mo/Al2O3 and Ni-Mo/Al2O3.
10. The process as claimed in claim 1 or claim 2, wherein said hydrocarbon feedstream is at least one of naphtha, kerosene, diesel, petrol, jet fuel, and lubricating oil.