Description:Field of the Invention
The present invention relates to a process for making low aromatic and ultra-low sulfur jet fuel for air breathing engine applications. More particularly, the present invention is related to a process for making fuel composition usable as propellant in air breathing engines with Mach 3+ speed. In one of feature, the present invention relates to a process for making liquid fuel composition. The said fuel composition contains mixture of hydrocarbons that boils in the range of kerosene. This kerosene range fuel contains less than 5% v/v of aromatics and 1-10 ppm of Sulfur by mass.

Background of the Invention
Supersonic jets cruise at very high speed of Mach 3 or higher, that usually require advanced propulsion fuels such as JP-4, JP-5, JP-7, JP-8 with special properties. Amongst the jet fuels, JP-7 is a low sulfur and low aromatic jet propellant used for air-breathing engine applications. At speeds as high as Mach 3-5, friction caused by air will generate high skin temperature of airframe and engine parts. Hence, the propellant should possess low vapor pressure or volatility so that it resists quick flashing at high temperature and exhibits good thermal oxidation stability, thereby acting as a heat sink for the system. The fuel has to be usable at wide range of temperatures, varying from near freezing at high altitudes, to high temperature conditions due to Mach 3+ speed.

The feedstock from refinery means hydrocarbon mixtures that are obtained from refining processes of crude oil. Generally, these hydrocarbon mixtures are classified depending upon the boiling range such as light, middle and heavy distillates. The light and middle distillates obtained from atmospheric distillation of crude oil are Naphtha, Kerosene and Diesel. Among these distillates, kerosene range cut is used as fuels for jet engines. The kerosene range cuts are collected from different plants such as crude distillation and hydrocracker units. The kero cut obtained from these units contains aromatic components and sulfur in the form of alkyl sulphides, thiophenes and benzothiophenes at varying levels that depends upon the crude and processing plants. In general, aromatics in hydrocarbon fuel will impart poor oxidation stability and restricts its use in high-end applications such as Mach 3+ engines. Additionally, sulfur in the feed has to be removed in order to meet environmental regulations.

Thus, the kerosene feedstock obtained from different sources as mentioned above has to be processed for the removal of aromatic and sulfur contents in order to meet the required specifications. Several open and patented literatures are available on the reduction of aromatic and sulfur contents in hydrocarbon feedstock and hydrogen is generally being used for achieving the same.

US10,246,652B2 discloses dearomatization of petroleum cuts using catalytic hydrogenation process. This prior art involves continuous dearomatization process of petroleum fractions to obtain low sulfur and very low aromatic content wherein any one stage of the process is operated at a temperature in the range of 80 to 180°C and pressure in the range of 60 to 160 bar. The product contained very low aromatic content generally lower than 300 ppm, preferably less than 100 ppm and more preferably less than 50 ppm.

EP0794241A2 discloses the hydrogenation of naphthenic cut for dearomatization process. EP0794241A2 claimed for hydrogenation of a middle distillate (180 to 320°C) with specific gravity of 0.810 in the presence of an active HTC-400 type nickel catalyst. The process was carried out under 40 bar hydrogen pressure and temperature range of 130 to 162°C. The product aromatic content was reduced from 25 to 0.5 % by volume.

DE19704128A1 claimed for hydrogenative dearomatization of a stream of reformates. The process was executed in the presence of nickel-containing catalyst and treating temperature range of 70 to 200°C, hydrogen pressure of 25 to 40 bar. The initial feed streams with aromatic content of 2 to 30% by weight were treated to obtain dearomatized streams containing not more than 0.05% by weight.

CN106661464B discloses a process for the dearomatization of petroleum fractions (boiling point range of 100 – 400°C) by hydrogenation process. The dearomatization cycle was carried out under a pressure of 20 to 200 bar and temperature of 80 to 300°C. The dearomatized stream was found to have aromatic content less than or equal to 300 ppm.

The hydrocarbon fuel with high aromatic content is harmful in nature and sulfur in the feed must be removed in order to meet environmental regulations. Thus, there is a need to develop a process to achieve the goal of meeting JP-7 fuel quality specification with less aromatics and sulfur content.

Objects of the Invention
The principal object of this invention is to develop a process for converting refinery feedstock to an advanced jet fuel that is equivalent to JP-7.

Another object of this invention is to remove sulfur (<10 ppm) in the hydrocarbon feed in order to meet environmental regulations.

A further object of this invention is to develop a process to achieve the goal of meeting JP-7 fuel quality specification with aromatics less than 5% by volume.

A further object of this invention is to develop a process to reduce the aromatic content of JP-7 fuel (consisting of <5% v/v) to less than 1% v/v (deep dearomatization of JP-7) to produce a fuel exhibiting rocket propellant (RP-1) characteristics.

Summary of the Invention
Vacuum Gas Oil, both light and heavy ends (LVGO and HVGO) were hydrotreated and hydrocracked to produce wide range of hydrocarbon mixtures viz., C1-C2 hydrocarbons, LPG and various liquid streams that are fractionated to individual cuts based on boiling points. Amongst the different streams, the product mixture boiling between 130°C and 375°C is utilized in the present invention.

The product mixture was pumped into a fractionator to produce a feed cut having initial boiling point (IBP) of 170°C and final boiling point (FBP) of 290°C.

The above obtained fractionate was distilled again as per ASTM Method in True Boiling Point (TBP) Apparatus to get a desired cut with IBP of 188°C and FBP of 270°C. The fractionate thus obtained above is used as feedstock in the making of JP-7 fuel. This feedstock contains about 10 weight percent of aromatics.

The feed was subjected to treatment under hydrogen atmosphere to facilitate the removal of aromatic content through saturation process. The aromatic saturation of the feed was carried out in vertical column reactor using hydrogenation catalyst. Typically, nickel supported on silica-alumina catalyst was used for this process. The operating conditions like temperature, pressure and liquid hourly space velocity (LHSV) were studied to produce JP-7 equivalent fuel with required specification.

Detailed Description of the Invention
Those skilled in the art will be aware that the present disclosure is subject to variations and modifications other than those specifically described. It is to be understood that the present disclosure includes all such variations and modifications. The disclosure also includes all such components of the composition, steps of the process, features of the composition, referred to or indicated in this specification, individually or collectively, and any and all combinations of any or more of such components or steps or features.

Definitions
For convenience, before further description of the present disclosure, certain terms employed in the specification, and examples are collected here. These definitions should be read in the light of the remainder of the disclosure and understood as by a person of skill in the art.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure, the preferred methods, and materials are now described. All publications mentioned herein are incorporated herein by reference.

The present disclosure is not to be limited in scope by the specific embodiments described herein, which are intended for the purposes of exemplification only. Functionally equivalent products and processes are clearly within the scope of the disclosure, as described herein.

‘VGO’ is the acronym of Vacuum Gas Oil having boiling range between 370 to 550°C, and is generated from Vacuum Distillation Unit.

‘LVGO’ is the acronym of Light Vacuum Gas Oil having boiling range between 370 to 400°C, and is generated from Vacuum Distillation Unit.

‘HVGO’ is the acronym of Heavy Vacuum Gas Oil having boiling range between 400 to 550°C, and is generated from Vacuum Distillation Unit.

Mach 3+ speed: The speed of sound, under standard conditions, is 1235 kmph. Mach 3 is three times the speed of sound, or about 3700 kmph.

JP-7 is a jet fuel developed by the U.S. Air Force for use in supersonic aircraft because of its high flashpoint and thermal stability. JP-7 is not a distillate fuel but is created by blending stocks in order to have very low concentration of highly volatile components and almost no sulfur, oxygen, and nitrogen impurities.

True Boiling Point (TBP) Apparatus is used to obtain the distillation curve for a crude oil sample by distilling the crude oil into a number of narrow fractions up to 400 °C.

Air breathing engines are a type of jet propulsion engines in which the engines use oxygen from the atmosphere for the combustion of fuel.
Net heating value of combustion is the quantity of energy released when a unit mass of fuel is burned at constant pressure, with all of the products, including water, being gaseous.
In hydrotreating process, the heteroatoms such as S, N, and metal impurities Ni, V etc., present in the feed (VGO) are removed usually operated at around 140-160 kg/cm2 H2 pressure and 300-400°C. During this process, in addition to the removal of these impurities, olefins & aromatic saturation occurs to obtain 8-10% v/v aromatic content.
During hydrocracking process, the larger molecules (carbon chain) are cracked to smaller molecules thereby boiling range of the feed is reduced to about 50-100 units under similar condition like hydrotreating process using specific catalyst.
Aromatic compounds existing in petroleum distillate fractions are undesirable in refineries because saturating the aromatic substances necessitates huge consumption of hydrogen thereby leading to cost heavy operations. The products with high aromatic content are harmful in nature and hence removal of these aromatics will improve the product quality and at times leads to the development of new products such as special solvents or fuels. De-aromatization techniques for removing / reducing the aromatic contents in petroleum fractions like solvent extraction, hydrogenation / reduction processes are well established. Hydrogenation process in the presence of suitable catalyst at elevated temperature and hydrogen pressure leads to improvement in removal efficiency of aromatics.

Accordingly, the present invention provides a process for converting vacuum gas oil to a hydrocarbon fuel composition, wherein the process comprises:
(a) converting vacuum gas oil (VGO) to a cut stream that can boil between 130°C-375°C and an unconverted oil;
(b) fractionating the cut stream obtained in step-(a) to obtain a fractionate having specified cut range with initial boiling point (IBP) of 170°C and final boiling point (FBP) of 290°C;
(c) distilling the fractionate obtained in step-(b) in True Boiling Point (TBP) apparatus to get a final cut to match the IBP and FBP of JP-7; and
(d) saturating the final cut obtained in step-(c) to remove aromatics through hydrogenation process to obtain the hydrocarbon fuel composition having aromatics in the range 0.1 - 5% by volume and 1-10 ppm sulfur by mass.

In one of the features of the present invention, the fractionate obtained from step-(b) is distilled to obtain distillate having density in the range of 0.7700-0.8300 g/cc and preferably in the range of 0.800-0.822 g/cc, flash point as high as 60 to 80°C and mostly over 70°C and freezing point as low as -43°C to -60°C and mostly around/less than - 50°C.

In another feature of the present invention, the fractionate is distilled in True Boiling Point (TBP) apparatus to get the final cut with IBP of 188°C and FBP of 270°C.

In yet another feature of the present invention, the cut stream obtained from step-(a) is fractionated to obtain fractionate with IBP above 180°C, 10% recovery between 195°C - 205°C, 20% recovery between 205°C-210°C, 90% recovery between 250°C - 260°C and FBP up to 290°C as per ASTM D86 method.

In yet another feature of the present invention, the final cut obtained from step-(c) is hydrogenated to remove the aromatics through saturation thereby producing the hydrocarbon fuel composition containing 0.1 - 5 vol% of aromatics and more precisely in the range of 3-4 vol% or <1 vol% and 1-10 ppm or < 1 ppm of sulfur by mass depending upon the purpose of use.

In yet another feature of the present invention, the hydrocarbon fuel composition is obtained from hydrogenation process wherein the reaction temperature ranges between 75°C to 300°C preferably in the range of 150-220°C at which the maximum product yield and aromatic saturation were obtained.

In another feature of the present invention, the final cut obtained in step-(c) comprises hydrocarbon feed and during the hydrogenation process, hydrogen to hydrocarbon feed molar ratio was kept between 2.5 and 250 and most preferably in the range of 25 to 250 to achieve maximum aromatic saturation.

In yet another feature of the present invention, the hydrocarbon feed is pumped to attain Liquid Hourly Space Velocity (LHSV) in the range of 1h 1 to 5h-1.

In yet another feature of the present invention, in the hydrogenation process, hydrogen pressure is maintained between 2 to 40 bar and most preferably between 25 to 40 bar to achieve maximum aromatic saturation in the product (0.1 - 5 vol% of aromatics).

In one of the features of the present invention, the hydrogenation process is occurred in presence of Ni loaded silica-alumina catalyst (NiO/SiO2-Al2O3).

The present invention is primarily related to a process involving more than one step to achieve the goal of meeting JP-7 fuel quality specification with aromatics less than 5% by volume. The fuel should also have a net heating value of combustion of at least 43.5 MJ/kg and a density over 0.8 g/cc. It should also exhibit low freezing point and high flash point characteristics. In order to meet the target fuel specification, the reduction of aromatic content to less than 5% in the hydrocarbon composition is one of the essential properties to be worked out in this present invention. The aromatic reduction was carried out in the presence of Ni-based catalyst under hydrogen atmosphere. The other desired properties such as flash point, boiling range (initial boiling point, IBP & final boiling point, FBP), sulfur content and freezing point are also required to be tailored to stipulated level thereby enabling the final hydrocarbon composition to qualify as advanced jet fuel (JP-7). These desired properties were tailored in the hydrocarbon composition through fractionation processes. Overall, a mixture of hydrocarbon from a secondary process plant was identified to meet the requirement. The selected mixture was suitably fractionated to obtain a product, which was a feed for further process to reduce the aromatic content by hydrogenation step. The feed was processed under high pressure hydrogen environment in the presence of nickel based catalyst to reduce the aromatic content.

EXAMPLES:
Having described the basic aspects of the present invention, the following non-limiting example illustrates the specific embodiments thereof. Those skilled in the art will appreciate that many modifications may be made in the invention without changing the essence of invention.

Example 1
The feed used in this invention is drawn from a commercial plant. This plant converts VGO to lighter hydrocarbons through hydrotreating and hydrocracking process. The product especially in the boiling ranges 130°C and 375°C is drawn from the plant. The product mixture was pumped into a fractionator to produce a fractionate having a cut range with initial boiling point (IBP) 170°C and final boiling point (FBP) 290°C. The physical Properties of fractionate obtained from the plant are given below in Table 1. The above fraction is used for further processing to produce desired fuel composition with characteristics equivalent to JP-7.

Table 1: Physical Properties of Fractionate obtained from the plant
S.N. Test ASTM Test Method Feed Results
1. Aromatics, Vol % HPLC 8.3
2. Sulphur, ppm D1266 0.36
3. Flash point, °C D93 62
4. Freezing point, °C D2386 - 57
5. Density @ 15°C, g/cc D1298 0.8202
6. Fractionation/Distillation Temperature, °C
Initial boiling point
10 percent recovered
20 percent recovered
90 percent recovered
End Point
D86
170
189
193
251
290

Example 2
The sample obtained in example 1 is subjected to distillation in TBP apparatus as per ASTM method D2892 to prepare distillate with IBP and FBP matching that of JP-7. About 15L of sample from Example 1 was taken in TBP distillation unit under 760-100 Torr pressure and distilled to produce a feed with boiling range similar to that of JP-7. The product obtained from TBP is tested for boiling point property as per ASTM D86 method and the results are given below in Table 2.

Table 2: Boiling range property of JP-7 feed
Distillation Temperature, °C ASTM Test Method Feed Results

Initial boiling point
10 percent recovered
20 percent recovered
90 percent recovered
End Point D86
188
202
206
254
270

Example 3
Hydrogenation of aromatic content in the feed stock prepared through Example 2 is carried out over supported metal catalyst. The catalyst properties are mentioned in the Table 3. The choice of catalyst was based on the feedstock nature and required activity/selectivity of the reactions. Based on the low ‘N’ and ‘S’ in the feed, Ni loaded silica-alumina catalyst was selected.

The catalyst chosen for the reaction selectively promotes the desired hydrogenation reaction and suppresses undesirable reaction. The spent catalysts can be regenerated, reactivated, rejuvenated and restored to fresh catalyst condition and made ready for another operating cycle.

Table 3: Properties of Hydrogenation Catalyst
Catalyst NiO/SiO2-Al2O3
Catalyst Type Regenerative
Catalyst Shape Extrudates
Surface Area, m2/g 175
Total pore volume, cc/g 0.35
Density, g/cc 0.7
Crushing Strength, N 3.5

Example 4
The present process involves the direct saturation of aromatics under hydrogen atmosphere in the fractionated feed into cycloparaffins in the presence of a hydrogenation catalyst consisting of nickel supported on silica-alumina.

The reaction was conducted at varying operating parameters to fix the optimized reaction conditions viz; temperature in the range between 75°C to 300°C, 2 to 40 bar pressure and LHSV (liquid hourly space velocity) in the range between 1 to 5 hr-1 under flowing hydrogen stream (1-30 standard litres per hour (SLPH)). Molar ratio of hydrogen to hydrocarbon is kept between 2.5 and 500. All the parameters are varied to obtain optimized condition to achieve maximum yield of fuel composition equivalent to JP-7 quality.

Example 5
The dependency of aromatic saturation on space velocity was studied by carrying out experiments under varied range (1 to 5 h-1) of feed flow rate. The other parameters such as hydrogen to hydrocarbon ratio, amount of catalyst, hydrogen pressure and reaction temperature were kept constant. The desired level of aromatics (less than 5% by volume) is obtained in the product thereby meeting the quality of JP-7 fuel. The volume percentage of aromatic content had been decreased by decreasing the space velocity or flow rate.

Table 4: Effect of LHSV on Aromatics v/v%
LHSV,
hr-1 Aromatics,
v/v %
1 1.5
2 2.3
3 3.4
4 4.6
5 5.2

Example 6
The effect of process temperature on the extent of aromatic saturation under constant hydrogen pressure was studied by carrying out reactions at various reactor temperatures from 150 to 220°C while keeping hydrogen to hydrocarbon ratio and the amount of catalyst constant. The results had shown that the volume percentage of aromatics in the product was decreased by this process. Thereby, the desired aromatic content (< 5 % v/v) in the product was achieved to match the quality of JP-7 requirement.

Table 5: Effect of temperature on Aromatics v/v %
Temperature,
°C Aromatics,
v/v %
150 7.1
160 5.9
170 4.6
180 3.3
190 3.3

Example 7
The saturation of aromatics in the feed under hydrogen atmosphere was carried out at various hydrogen pressures ranging between 25 and 40 bar while keeping the other parameters such as hydrogen to hydrocarbon ratio, temperature, catalyst amount and LHSV constant. In this way, the aromatic saturation was improved to the desired level (< 5% v/v) to meet the required specification of JP-7.

Table 6: Effect of Pressure on Aromatics v/v %
Pressure,
Kg/cm2 Aromatics,
v/v %
25 3.9
30 3.4
35 3.3
40 3.3

Example 8
A product obtained by following the fractionation procedure as per example 1 was found to have aromatic content of 4.85% and exhibiting other characteristics of JP-7 fuel quality. This sample was treated in the presence of nickel catalyst under 30 bar hydrogen pressure by following the reaction procedure as per example 6. The aromatic content in the resultant product had been reduced to 0.3% by volume. , Claims:1. A process for converting vacuum gas oil to a hydrocarbon fuel composition, wherein the process comprises:
(a) converting vacuum gas oil (VGO) to a cut stream that can boil between 130°C-375°C and an unconverted oil;
(b) fractionating the cut stream obtained in step-(a) to obtain a fractionate having specified cut range with initial boiling point (IBP) of 170°C and final boiling point (FBP) of 290°C;
(c) distilling the fractionate obtained in step-(b) in True Boiling Point (TBP) apparatus to get a final cut to match the IBP and FBP of JP-7; and
(d) saturating the final cut obtained in step-(c) to remove aromatics through hydrogenation process to obtain the hydrocarbon fuel composition having aromatics in the range 0.1 - 5% by volume and 1-10 ppm sulfur by mass.

2. The process as claimed in claim 1, wherein the fractionate obtained from step-(b) is distilled to obtain distillate having density in the range of 0.7700-0.8300 g/cc, flash point in the range of 60 to 80°C and freezing point in the range of -43°C to -60°C.

3. The process as claimed in claim 1, wherein the fractionate is distilled in True Boiling Point (TBP) apparatus to get the final cut with IBP of 188°C and FBP of 270°C.

4. The process as claimed in claim 1, wherein the cut stream obtained from step-(a) is fractionated to obtain fractionate with IBP above 180°C, 10% recovery between 195°C - 205°C, 20% recovery between 205°C-210°C, 90% recovery between 250°C - 260°C and FBP up to 290°C as per ASTM D86 method.

5. The process as claimed in claim 1, wherein the final cut obtained from step-(c) is hydrogenated to remove the aromatics through saturation thereby producing the hydrocarbon fuel composition containing 0.1 - 5 vol% of aromatics and 1-10 ppm of sulfur by mass depending upon the purpose of use.

6. The process as claimed in claim 5, wherein the hydrocarbon fuel composition is obtained from hydrogenation process wherein the reaction temperature ranges between 75°C to 300°C at which the maximum product yield and aromatic saturation were obtained.

7. The process as claimed in claims 1-6, wherein the final cut obtained in step-(c) comprises hydrocarbon feed and during the hydrogenation process, hydrogen to hydrocarbon feed molar ratio was kept between 2.5 and 250 to achieve maximum aromatic saturation.

8. The process as claimed in claims 1-7, wherein the hydrocarbon feed is pumped to attain Liquid Hourly Space Velocity (LHSV) in the range of 1h 1 to 5h-1.

9. The process as claimed in claims 1-8, wherein in the hydrogenation process, hydrogen pressure is maintained between 2 to 40 bar to achieve maximum aromatic saturation in the product (0.1 - 5 vol% of aromatics).

10. The process as claimed in claim 1, wherein the hydrogenation process is occurred in presence of Ni loaded silica-alumina catalyst (NiO/SiO2-Al2O3).