WO2006088314A1

WO2006088314A1 - Process for producing ultra low sulfur and low aromatic diesel fuel

Info

Publication number: WO2006088314A1
Application number: PCT/KR2006/000528
Authority: WO
Inventors: Ik Sang Yoo; Myung Jun Kim; In Ho Cho; Cheol Woo Park; Gyoo Tae Kim; Jae Wook Ryu; Jee Sun Shin; Sung Bum Park
Original assignee: Sk Energy Co., Ltd.
Priority date: 2005-02-17
Filing date: 2006-02-15
Publication date: 2006-08-24
Also published as: KR20060091990A; CN101120075B; KR101156370B1; CN101120075A; JP2008530336A

Abstract

On the basis of the finding that hydrogenation reactivity with aromatics, as well as desulfurization reactivity, is closely correlated with the distillation properties of feedstock straight-run gasoil, the disclosed process is provided for separating the straight-run gasoil effluent from a crude distillation unit so as to afford a feedstock having properties good enough to be treated in a post-hydrodesulfurization process, thereby not only utilizing pre-existing hydrodesulfurizaion units to the maximum, but also significantly reducing aromatic levels. The process allows the production of diesel fuel meeting the WWFC category-4 standard, requiring the minimum possible investment in new facilities.

Description

[DESCRIPTION]

[Invention Title]

PROCESS FOR PRODUCING ULTRA LOW SULFUR AND LOW AROMATIC DIESEL FUEL

[Technical Field]

The present invention relates to a process for producing ultra low sulfur diesel fuel through a hydrogen addition catalytic reaction. More particularly, the present invention relates to a process for producing ultra low sulfur and low aromatic diesel fuel, in which the straight-run gasoil effluent from a crude distillation unit is separated to afford a feedstock having properties good enough for it to be treated in a post- hydrodesulfurization process, thereby not only utilizing pre-existing hydrodesulfurizaion units to the maximum, but also significantly reducing aromatic levels.

[Background Art] Nowadays, although various substitute energy sources are actively exploited in order to improve air quality and prevent global warming, it is expected that gasoline and diesel fuels will continue to dominate the automobile fuel market, which gradually increases every year, for a considerable period of time. However, the market requires high quality fuels in response to the movement for improving the global environment. Particularly, diesel will be regulated to contain sulfur in amounts as low as 50 or 10 ppm in advanced nations and other nations starting in 2005 or 2010. For instance, fuels for sale in the European Union must have a sulfur content of 50 wppm or less. According to the EPA' s regulation, which comes into effect on June 1, 2006, the sulfur content of diesel must be reduced to 15 wppm or less. Afterwards, European and major Asian nations are expected to enact regulations similar to that of the EPA' s. Besides sulfur, aromatic compounds including multi-ring have become targets for restriction. In fact, regulations are now in force, stipulating that the total amount of aromatic compounds be reduced to a certain level. For example, the maximum allowable total aromatics level for CARB (California Air Resources Board) reference diesel and Swedish Class I diesel are 10 vol% and 5 vol%, respectively. In the near future, regulations with regard to fuel properties, such as aromatic content, distillation property, etc., are expected to become more severe or to be newly enacted.

Since 2000, new desulfurization processes based on adsorption, solvent extraction, etc. have been developed in order to produce ultra low sulfur diesel having a sulfur content of 50/10 ppm or less. However, oil refining companies prefer the use of already developed desulfurization processes over the development of new processes. Most oil refining companies have met the regulation of sulfur content by improving the performance of desulfurization catalysts or modifying processes. By way of preparing for the possibility that regulations for aromatics or distillation be introduced, however, no alternatives, except for a few process techniques, have been suggested. Now, oil refineries are confronted with a new investment load and huge economic loss on management.

Examples of representative process techniques include a SynSat process developed in the early 1900 to reduce sulfur and aromatic levels, and an HDS-HAD process, developed around 2000 on the basis of HAD (hydro-dearomatization) catalysts. However, these process techniques suffer from the disadvantages of increasing the operation cost due to excessive amounts of hydrogen consumed and requiring huge investment for the modification of pre-existing desulfurization processes or for the introduction of new process facilities. Korean Pat. Laid-Open Publication No. 98-64338 discloses that the sulfur content of straight run gasoil can be lowered to 100 ppm or less by hydro- desulfurization in the presence of a catalyst comprising a mineral support, a Group VIB metal, a Group VIII metal, and phosphorus (step 1), and that if at least part of the steam stripping stream from the effluent of step 1 is allowed to pass, along with hydrogen, through a catalyst bed in which VIII metal and halogen are impregnated into a mineral support, an aromatic content less than 5 vol% and a sulfur content less than 50 ppm (preferably, 10 ppm) can be achieved.

U. S. Pat. No. 6,824,673 discloses a process for producing diesel having a sulfur content of 10 wppm or less and a total aromatic amount of 15 wt% or less. This process, aiming to overcoming the problem of conventional hydrodesulfurization/aromatic saturation processes that require high pressures for operation, comprises the treatment of a distillate feedstock in a first hydrodesulfurization stage in the presence of a hydrogen-containing treatment gas and a hydrodesulfurization catalyst to partially desulfurize the feedstock. The stripped liquid phase stream is then treated in a second hydrodesulfurization stage, also in the presence of a hydrogen-containing treatment gas and a hydrodesulfurization catalyst. After being transferred to an aromatic hydrogenation stage, the stripped liquid phase stream is reacted with a hydrogen-containing treatment gas in the presence of an aromatic hydrogenation catalyst to hydrogenate the aromatics thereof. This process, however, as described, requires the addition of many process stages and considerably alters pre-existing processes, thus not overcoming the problem of conventional processes in terms of process convenience and economic benefit.

Of course, the above-mentioned high-cost processes, if suitable for the properties of individual oil refining companies, may be needed for some companies.

However, it is preferred that the already developed deep desulfurization processes of oil refining companies be utilized as much as possible, as in the case of sulfur content restriction.

Additionally, it is anticipated that ultra low sulfur diesel be required to show light oil characteristics in distillate as well as to have low total aromatics levels. In response to such anticipation, diesel needs to meet the standards of WWFC (world wide fuel charter) category 4 shown in Table 1, below.

TABLE 1

Therefore, there is a need for the development of a process that assures the production of diesel satisfying the standards of WWFC category 4, as well as utilizing pre-existing production facilities for ultra low sulfur diesel. In addition, it is economically favorable to utilize heavy gasoil distillates having high boiling points, amounting to as much as 20-30 wt% of the straight run light gasoil in the straight gasoil obtained from an atmospheric distillation unit, for the production of half-finished diesel products by taking advantage of pre-existing facilities for ultra low sulfur diesel.

[Disclosure] [Technical Problem]

The development of an economically favorable process has been suggested, as described above, in response to the direction of development of diesel automobile engines to meet the requirement for fuels which are ultra low in sulfur content and show distillate light oil characteristics and narrow cut aromatic properties.

Leading to the present invention, intensive and thorough study on the properties of hydrogen addition reactions, especially process conditions in a deep desulfurization zone, distillation characteristics of feedstock and reaction behaviors depending on catalyst properties, conducted by the present inventors with the aim of utilizing pre-existing deep desulfurization processes as much as possible while meeting the diesel standards of WWFC category 4, resulted in the finding that hydrogenation reactivity with aromatics, as well as desulfurization reactivity, is closely correlated with the distillation properties of the feedstock straight run gasoil. That is, as the distillation range is lowered below a certain temperature point, straight run gasoil, which is used as hydrodesulfurization process feedstock, is able to have its sulfur content easily decreased from around 10 ppm to 5 ppm as well as to have its aromatics content significantly reduced in deep desulfurization conditions. Additionally, the present inventors developed an effective design in which distillates having a certain boiling point or lower are separated from the straight run gasoil and used as hydrodesulfurization process feedstock while the residual heavy distillates of high boiling points are produced into half-finished diesel products.

Therefore, it is an object of the present invention to provide a process for the production of diesel, which allows for simultaneous reduction to ultra low sulfur levels and significant low aromatic levels, in deep desulfurization conditions.

It is another object of the present invention to provide a process for producing ultra low sulfur and low aromatic diesel fuel, which can maximally utilize pre-existing deep sulfurization process facilities and requires a minimum of new investment therein, requiring neither the mass-scale modification of pre-existing process facilities nor the introduction of new process facilities.

It is a further object of the present invention to provide a process in which light gasoil distillate having a certain boiling point or less is separated from straight- run gasoil so as to be used as feedstock for hydrodesulfurization while the remaining gasoil distillate is used for producing half-finished diesel products.

[Technical Solution]

In accordance with an embodiment, the present invention provides a process for producing low aromatic and ultra low sulfur diesel fuel, comprising: a) separating the straight-run gasoil effluent from a crude distillation unit into distillates on the basis of a cut point set in a range from 320 to 36O⁰C; b) subjecting the distillates with the cut point or less to hydrodesulfurization in the presence of a hydrodesulfurization catalyst under a condition including a pressure of 30-80 kg/cm², a temperature of 320-38O⁰C, a liquid hourly space velocity of 0.1-2.0 hr^"1, and an H₂/oil ratio of 150-1000 Nm³/kl; and c) recovering a gas oil distillate that has undergone the hydrodesulfurization of step b). In a preferred modification, the process further comprisesireforming at least a part of the gasoil distillate having a boiling point exceeding the cut point by means of selective hydrocracking; nitrogen adsorption/dewaxing/hydrodesulfurization; or hydro-desulfurization/dewaxing processes; and separating a light gasoil distillate from a stream obtained after the reforming step and pooling the diesel distillate with the light gasoil distillate obtained in step b). The distillate remainder after the separation of diesel distillate from the stream effluent from the post-treatment process can be used as feedstock for other processes.

[Advantageous Effect] Featuring the hydrodesulfurization of the distillate obtained from the straight- run gasoil effluent from a CDU at a cut point set within the boiling point range of the straight-run heavy gasoil or less in deep desulfurization conditions, the process in accordance with the present invention brings about a significant reduction in aromatic levels as well as achieving the ultra low sulfur level meeting the standard imposed by advanced nations. Particularly, the process of the present invention enjoys the advantage of maximally utilizing pre-existing deep sulfurization process facilities and requiring minimal investment therein, requiring neither major modification of preexisting process facilities nor the addition of new process facilities. In addition, the present invention can decrease the reaction temperature required for the achievement of a predetermined sulfur level, thereby extending the life span of the catalyst used and reducing the hydrogen amount consumed. Further, a distillate with boiling points exceeding the cut point can be converted into clean half-finished diesel products through suitable reforming processes, as well.

[ Description of Drawings ]

FIG. 1 is a conceptual view showing a process for treating straight-run gasoil in a separate process so as to maximize the efficiency of a post-process in accordance with the present invention;

FIG. 2 is a graph in which the distribution of nitrogen compounds in straight run gasoil is plotted against boiling points;

FIG. 3 is a schematic process view showing a strategy for reforming a gasoil distillate separated from the straight-run gas oil at a boiling point exceeding the cut point through a selective hydrocracking process in accordance with an embodiment of the present invention; FIG. 4 is a schematic process view showing a strategy for reforming a gasoil distillate separated from the straight-run gas oil at a boiling point exceeding the cut point through nitrogen adsorption/dewaxing/hydro-desulfurization processes in accordance with another embodiment of the present invention;

FIG. 5 is a schematic process view showing a strategy for reforming a gasoil distillate separated from the straight-run gas oil at a boiling point exceeding the cut point through hydro-desulfurization/dewaxing processes in accordance with a further embodiment of the present invention;

FIG. 6 is a graph in which saturation rates of mono-aromatic compounds in a base distillate and a 340°C-distillate are plotted against reaction temperatures, obtained in Example 3;

FIG. 7 is a graph showing saturation rates of mono-aromatic compounds in a base distillate, a 340°C-distillate and a 360°C-distillate, obtained in Example 3; and FIG. 8 is a graph in which saturation rates of mono-aromatic compounds are plotted against reaction temperatures according to the CoMo catalyst and the CoMo- NiMo [90- 10] catalyst, obtained in Example 4.

* Brief description of reference numerals*

1, 11, 21: crude oil 2, 12, 22: distillates lighter than straight-run gasoil

3, 13, 23: distillates of straight gasoil having boiling points not higher than cut point

4, 14, 24: distillates of straight gasoil having boiling points exceeding cut point 5, 15, 25: atmospheric residual oil(AR)

6, 16, 26: hydrodesulfurized distillates having boiling points not higher than cut point

7: stream effluent from selective hydrocracking process (HDC)

17: stream effluent from N adsorption/dewaxing/hydro-desulfurization process

27: stream effluent from hydrodesulfurization/ dewaxing process

100, 110, 120: crude distillation units (CDU)

101, 111, 121: hydrodesulfurization (HDS) units

102: selective hydrocracking (HDC) unit 112: nitrogen adsorption/dewaxing/hydro-desulfurization unit 122: hydrodesulfurization/dewaxing unit 103, 113, 123: diesel storage unit

[BEST MODE]

Reference should now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures.

In search of a solution to the utilization of pre-existing deep desulfurization units in aromatic reduction, the present invention is, as described above, developed on the basis of the unexpected finding that the properties of feedstock, especially the heavy components of straight run gasoil, greatly influence the saturation or hydrogenation of aromatics as well as the reduction of sulfur levels under deep desulfurization conditions. Accordingly, the distillation properties of feedstock are optimized so as to overcome the problems of conventional processes, that is, the huge investment requirement and increased operation costs, and to maximally utilize preexisting deep desulfurization units, and the inevitable loss of diesel fuel is effectively compensated for by introducing a new process to produce clean diesel (half-finished) products having sulfur and aromatic levels meeting the standard of WWFC Category 4, thereby compensating for the inevitable loss of diesel.

To approach this end, serious consideration was taken of the following two aspects in the present invention. Most important is the knowledge of how distillates having high boiling points, which are usually generated upon the treatment of the straight run gasoil effluent from crude distillation units (CDU) in deep desulfurization conditions and cause catalyst degradation and difficulty in maintaining stable desulfurization performance, can be separated and treated so as to maximize the hydrogenation of aromatics as well as the reduction of sulfur levels. Additionally, a method is provided for utilizing gasoil having high boiling points, left after the separation, for the production of the half-finished clean diesel products, thereby gaining great economic benefit.

With reference to FIG. 1 , the concept of maximizing the efficiency of a post- process through the separate treatment of straight run gas is illustrated. FIG. 2 shows distribution properties of nitrogen (N) compounds in straight run gasoil plotted against boiling points.

The straight run gasoil of the distillates obtained from CDU upon fractional distillation usually has a boiling point from about 200 to 460°C, and typically from about 200 to 390°C, according to the ASTM D 86 standard. To be used as feedstock in the present invention, straight run gasoil preferably contains sulfur in an amount of about 2.0 wt% and has a nitrogen content of about 400 ppm or less.

The term "hydrodesulfurization reaction or process" as used herein means a reaction or process which is effected with hydrogen-containing treatment gas in the presence of a catalyst able to remove hetero-atoms, particularly sulfur and nitrogen atoms, from feedstock, and to hydrogenate aromatics.

In the present invention, serving as classification standards for refractory sulfur (RS) compounds based on the dibenzothiophene (DBT) structure, distribution properties over a TBP(true boiling point) cut range of each group of methyl substitutes are important factors to determine temperature criteria for separating straight-run gasoil. Representative of RS compound are dibenzothiophene derivatives such as A- methyl dibenzothiophene, 4,6-dimethyl dibenzothiophene, etc.

Of the RS compounds, DBTs, having one or no methyl substitutes (IC- DBTs) are very easy to desulfurize and are distributed at 32O⁰C or less on the basis of fractional distillation. DBTs are distributed predominantly within a temperature range from about 320 to 34O⁰C when two methyl substitutes (2C-DBTs) are present, within a temperature range from about 340 to 36O⁰C when three methyl substitutes (3C-DBTs) are present, and within a temperature range higher than 36O⁰C if four or more methyl substitutes are present.

In the distillation range of 36O⁰C or higher, as seen in FIG. 2, the concentration of both nitrogen compounds, having significant influence on 4,6- DMDBT deep desulfurization, and RS compounds such as high boiling point benzo- DBTs, sharply increases. Particularly, studies on deep desulfurization demonstrated that distillates having a boiling point higher than 36O⁰C, even if contained in a trace amount, aggravate desulfurization conditions, and in particular cause a rapid increase in reaction temperature, reducing the catalyst life span from four or five years to one or two years.

In accordance with the present invention, a suitable cut point of straight-run gasoil is chosen in consideration of the above-mentioned analysis results. As seen in FIG. 1, straight-run gasoil is divided into straight-run light gasoil and straight-run heavy gasoil typically on the basis of a boiling point of 38O⁰C. However, it should be understood that this discrimination is set for the sake of convenience in light of the overall context, but is not intended to limit the present invention. In the embodiment shown in FIG. Ia, straight-run light gasoil may be divided into distillates having boiling points not less than and not more than the chosen boiling point (that is, cut point). The distillate exceeding the chosen boiling point is a mixture of a heavy distillate of the straight-run light gasoil and the straight-run heavy gasoil, and is subjected to a separate post-reformation process. In an embodiment of FIG. Ib, straight-run light gasoil is divided into distillates having boiling points not less than and not more than the chosen boiling point. The distillate exceeding the chosen boiling point is subjected to a separate post-reformation process.

Of all of the straight-run gasoil, thus, the distillates below the chosen boiling point can be hydrodesulfurized in a deep desulfurization condition using pre-existing process units. Meanwhile, at least part of the distillates exceeding the chosen boiling point are treated in a separate post-reformation unit. Hence, this strategy according to the present invention can greatly reduce the required facility investment compared to conventional process techniques, thereby solving the economic problem of total additional investment.

In accordance with the present invention, the cut point, which is the criteria for dividing straight-run gasoil, is set at a maximum of about 36O⁰C, in consideration of the distillation properties of straight-run gasoil. If necessary, the cut point may be decreased down to about 32O⁰C. Therefore, the cut point is preferably set in the range from about 320 to 360⁰C. When account is taken of the distribution properties of RS compounds, the cut point is more preferably set at about 340⁰C.

The distillate below the chosen cut point is treated in a hydrodesulfurization stage. In this regard, typical deep desulfurization conditions are preferred because it allows maximum use of pre-existing units. Such deep desulfurization conditions may include a reaction pressure of 30-80 kg/cm², a reaction temperature of about 320-38O⁰C, a liquid hourly space velocity (LHSV) of about 0.1-2.0 hr^"1, and an H₂/oil ratio of about 150-1000 Nm³/kl. Preferably, the deep desulfurization of the distillate below the cut point is performed at a reaction pressure of about 50-70 kg/cm³, a reaction temperature of about 350~370°C, an LHSV of about 0.5-1.0 hr^'1, and an H₂/0U ratio of 300-500 Nm³/kl. Under these conditions, the hydrodesulfurization is conducted to reduce sulfur levels below 10 ppm and preferably below 5 ppm. When the feedstock straight-run gasoil is divided on the basis of a certain boiling point (e.g., about 340°C) particularly in consideration of the distribution properties of RS compounds, the distillate obtained below the boiling point can be reduced in sulfur level to 5 ppm or less, and to as low as 1-2 ppm in some case. As will be apparent from the data of the following examples, the reaction temperature necessary for the reduction of sulfur levels to meet the criterion (for example, 10 ppm or less) can be decreased by 18⁰C or more. A typical catalyst for use in hydrodesulfurization comprises a porous refractory support (e.g., γ-alumina, silica, zeolite, or combinations thereof) on which a first metal component, identified as Mo and a second metal component, selected from a group consisting of Co, Ni, W, and combinations thereof, are deposited. The first metal component is used in an amount of about 10-30 wt% based on the total weight of the catalyst and preferably in an amount of about 12-20 wt%, while the second metal component amounts to about 2-10 wt%, and more preferably to about 3~7 wt% of the catalyst weight.

One of the most important features of the present invention, as described above, resides in that when distillates obtained below a predetermined boiling point from straight-run gasoil are hydrosulfurized under deep desulfurization conditions, their aromatic levels as well as sulfur levels can be significantly reduced. Particularly, to meet the WWFC Category-4 standard stipulating that an aromatic content be 15 wt% or less, the second metal component of the catalyst preferably comprises a combination of two or more metal ingredients, for example, CoMo-NiMo or CoMo- NiW, rather than a single ingredient. However, it is noteworthy that even when the second metal component is composed of a single ingredient (for example, CoMo), the distillates separated below a certain cut point have multi-ring aromatics, such as di- or more ring aromatics, decreased to 2 wt% or less, which is expected to be the standard for multi-ring aromatic levels in the future.

In accordance with the present invention, the distillates obtained at the chosen boiling point or less can be allowed to contain sulfur in an amount of 5 ppm or less and aromatics in an amount of 15 wt% or less when they are subjected to hydrodesulfurization under a deep desulfurization conditions. On the other hand, the distillates obtained at boiling points exceeding the chosen cut point are transferred into post-reformation processes where ultra low sulfur and low aromatic diesel fuels can be produced. These reforming processes can be effected through the three embodiments illustrated below. In this regard, FIGS. 3 to 5 suggest a selective hydrocracking process, a nitrogen adsorption/dewaxing/hydrodesulfurization process, and a hydrodesulfurization/dewaxing process, respectively, through which the gasoil distillates that obtained straight-run gasoil at boiling points higher than a predetermined cut point can be reformed.

Crude oil 1, 11, 21 is split into the components thereof in a crude distillation unit 100, 110, 120 according to boiling point by fractional distillation. While distillates 2, 12, 22 lighter than straight-run gasoil and distillates 5, 15, 25 heavier than straight-run gasoil are additionally separated, the distillate 3, 13, 23 obtained at or below a cut point from the straight-run gasoil is transferred to a hydrodesulfurization unit 101, 111, 121 operating under deep desulfurization conditions. The distillate 6, 16, 26 effluent from the hydrodesulfurization unit is recovered and carried into a diesel storage unit 103, 113, 123.

Meanwhile, the distillate 4, 14, 24 having a boiling point higher than the cut point is converted into higher valued fractions through a post-reformation process. In accordance with the present invention, as much distillate as possible is reformed into diesel fuel which meets the required low aromatic and ultra low sulfur standards and is then pooled, along with the distillate 6, 16, 26, in the diesel storage unit. In order to overcome the drawback of high boiling point distillates, that is, low temperature properties, a (hydro)dewaxing process may be conducted as shown in FIGS. 4 and 5. Representative reaction conditions in the selective hydrocracking unit 102, the nitrogen adsorption/dewaxing/hydrodesulfurization unit 112, and the hydrodesulfurization/dewaxing unit 122 are summarized in Table 2, below.

TABLE 2

¹ : In this HDC process, a conventional silica-alumina or zeolite based catalyst may be used.

: In this N adsorption process, a conventional silica gel, silica-alumina, or zeolite based adsorbent may be used.

: In this dewaxing process, a conventional zeolite-based catalyst may be used.

⁴: In this HDS process, the above-mentioned hydrodesulfurization catalyst may be used. In addition, a hydrotreating or hydrofinishing process may be further performed before or after the post-reformation process, so as to improve the color or stability of the product.

[Mode for Invention] A better understanding of the present invention may be obtained through the following examples which are set forth to illustrate, but are not to be construed as the limit of the present invention.

EXAMPLE 1

In this example, a description is given of the properties of various sample materials used and the yield change of straight-run light gasoil according to cut point. All the following sample materials were prepared from the same straight-run light gasoil, with the exception that the sample in the last column of Table 3 was a mixture with straight-run heavy gasoil. In Table 3, the main properties of the samples prepared from the distillates separated according to TBP cut points of 34O⁰C and 36O⁰C are given. In Table 4, the yields of light gasoil (LGO) are summarized according to various cut points. As understood from the data of Table 4, the yield is expected to change by about 5.6 vol % per 10⁰C of TBP cut point. However, since the properties, compositions and yields of the distillates are dependent on the properties of the crude oil used, the yield change is not intended to limit the scope of the present invention.

TABLE 3

34O⁰C+ distillate out of straight run light gasoil

: a mixture of 340°C+ distillate out of straight run light gasoil, and straight- run heavy gasoil

³: cloud point/pour point simulated distillation

TABLE 4

Light Gasoil (LGO) Yields According to TBP Cut Point

EXAMPLE 2

The three light gasoil species of Table 3 (base, 34O⁰C-, 36O⁰C-) were analyzed for desulfurization properties under the experimental conditions outlined in Table 5, below. Reaction experiments were performed in continuous type reactors to measure desulfurization temperatures and hydrogen consumption amounts necessary for the reduction of sulfur level to 10 ppm. The results are summarized in Table 6, below.

TABLE 5

Experimental Conditions

TABLE 6

As is apparent from the data of Table 6, when the distillates obtained from straight-run light gasoil at boiling points not more than the cut point set in the range from 320~340°C were subjected to hydrodesulfurization in deep desulfurization conditions, the reaction temperature necessary for the reduction of sulfur levels to 10 ppm or less could be decreased by 18⁰C or greater. In consideration of this result, the present invention is anticipated to prolong the life span of the catalyst by as much as 2 years and reduce hydrogen consumption by as much as 10%, compared to the case where straight-run gasoil is subjected to hydrodesulfurization without being separated according to distillation properties.

EXAMPLE 3

Changes in aromatic composition, monitored in Example 2, were given in Table 7, below. In addition, all of the base distillate, the 340°C-distillate, and the 360°C-distillate were measured for the saturation rate of mono-aromatic compounds according to reaction temperature, as well.

TABLE 7 Aromatic Levels

Saturation Rate of mono-aromatics: (Hydrogenation Conversion Rate)=[(A+B+C)-D]/(A+B+C) A: Concentration of di-aromatics in feedstock (wt%) B: Concentration of di-aromatics in product (wt%) C: Concentration of mono-aromatics in feedstock (wt%)

D: Concentration of di-aromatics in product (wt%)

As seen in FIG. 6, lower cut points of the straight-run gasoil resulted in higher hydrogen conversion rates of the mono-aromatic compounds. FIG. 7 shows saturation rates of mono-aromatic compounds in each of the base distillate, the 340°C-distillate, and the 360°C-distillate. At the same reaction temperature, the hydrogenation conversion rate of aromatic compounds increases as the distillation temperature of the straight-run gasoil decreases. However, as seen in FIG. 7, the increase of the hydrogenation conversion rate somewhat slowed in the range from 36O⁰C to 34O⁰C. It is believed that the slow increase rate is attributed to the hydrogen reactivity limit of the CoMo catalyst.

EXAMPLE 4 Instead of the catalyst containing CoMo (100%) as an active ingredient, a catalyst containing CoMo:NiMo(9:l) as an active ingredient was used for the desulfurization of the LGO of 360°C-distillate in the same conditions as in Example 2. As a result, a considerable decrease was brought about in the aromatic level of the produce. For comparison, the CoMo(100%) catalyst and the CoMo:NiMo(9:l) catalyst were analyzed for hydrogenation conversion rate and the results are given in FIG. 8. As shown in FIG. 8, the CoMo:NiMo (9:1) catalyst increases the conversion rate by as much as about 8 % on the basis of the same reaction temperature (36O⁰C), compared to the CoMo catalyst. The catalyst substitution enables the aromatic levels to be reduced to 15 % or less in given deep desulfurization conditions, as is apparent from the data of Table 7. Like this, the addition of NiMo can significantly improve the hydrogenation activity even at a low reaction temperature.

EXAMPLE 5

Experimental reactions were performed under the conditions shown in Table 8, below, in order to determine whether the distillates could be produced into diesel fuels by the reformation process including hydrocracking. The results are given in Table 9, below.

TABLE 8 Reaction Conditions for 34O⁰C^-(I)¹

¹ : all 3 steps are applied, on the basis of the inlet. The temperature at each step is determined by the inlet temperature and H₂ quench rates in consideration of the caloric value in each reactor, because the reaction in each reactor is exothermic. The reaction temperature is the weight average bed temperature (WABT) of each reactor.

²: Hydrotreating or hydrofϊnishing step. This may be performed at low temperatures using a conventional heat exchange net in order to improve the coloration and stability of the product.

TABLE 9

As shown in Table 9, the reformation of the distillate obtained from the straight-run gasoil at a boiling point higher than a chosen cut point resulted in the production of diesel fuels having a low aromatic level (15 wt% or less) and an ultra low sulfur level (10 ppm or less). In addition, the recovery rate into diesel distillate of the high boiling point distillates amounted to 82 vol%, thus showing a yield loss of as small as 6%. Accordingly, the process of the present invention is somewhat improved from an overall economic aspect, if additional naphtha production is considered.

EXAMPLE 6

In order to examine whether nitrogen ingredients could be effectively removed from the distillate obtained from the straight-run gasoil at higher than the cut point or more by adsorption as shown in FIG. 4, the 340°C+(l)distillate prepared in Example 1 was treated with modified silica adsorbent under the conditions of temperature of 70°C, LHSV of 1.5 hr^"1, and pressure of 7 kg/cm². The rate of removal of nitrogen from the distillate was measured to be 78% (total nitrogen level reduced from 526 ppm to 116 ppm).

Thus, it is expected that it is possible for the distillates to meet the requirements for low temperature properties and sulfur levels by employing the hydrodewaxing and hydrodesulfurizing catalyst modified according to the present

invention.

EXAMPLE 7

To examine whether the heavy gasoil could be produced into high quality diesel fuels when treated in combination with the straight-run light gasoil, the 340°C+(2) distillate prepared in Example 1 was tested under the conditions given in Table 10, below. TABLE 10 Reaction Conditions for 340°C+(2)¹

^!: the same condition as in Example 5, except for hydrogen partial pressure.

TABLE I l

Similar to that of Table 9 in Example 5, the data of Table 11 demonstrates that a mixture of the heavy gasoil and the high boiling point distillate of the straight- run gasoil can be produced into diesel fuel having a low aromatic level (15 wt% or less) and an ultra low sulfur level (10 ppm or less).

Examples are described in terms of the preferred embodiment of present invention. However, it should not be understood that such disclosure is not limited to explicit description of present invention. The description and the claims of present invention are to be interpreted as covering all alterations and modifications within the true scope of this invention.

Claims

[CLAIMS]

[Claim 1 ]

A process for producing low aromatic and ultra low sulfur diesel fuel, comprising: a) separating the straight-run gasoil effluent from a crude distillation unit into distillates on the basis of a cut point set in a range from 320 to 360°C; b) subjecting the distillates with the cut point or less to hydrodesulfurization in the presence of a hydrodesulfurization catalyst under a condition including a pressure of 30-80 kg/cm , a temperature of 320~380°C, a liquid hourly space velocity of 0.1-2.0 hr^'1, and an H₂/oil ratio of 150-1000 Nm³M; and c) recovering a gas oil distillate that has undergone the hydrodesulfurization of step b).

[Claim 2] The process as defined in claim 1, wherein the straight-run gasoil has a boiling point from 200 to 46O⁰C.

[Claim 3]

The process as defined in claim 2, wherein the straight-run gasoil has a sulfur level of 2 wt% or less and a nitrogen level of 400 wtppm or less.

[Claim 4]

The process as defined in claim 1, wherein the cut point is 340°C.

[Claim 5]

The process as defined in claim 1 , wherein the gasoil distillate obtained after step b) has a sulfur level of 10 ppm or less.

[Claim 6] The process as defined in claim 5, wherein the gasoil distillate obtained after the step b) has a sulfur level of 5 ppm or less.

[Claim 7]

The process as defined in claim 1 , wherein the gasoil distillate obtained after the step b) has a sulfur level of 5 ppm or less and an aromatic level of 15 wt% or less.

[Claim 8]

The process as defined in claim 1, wherein the hydrodesulfurization catalyst used in step b) comprises a porous refractory support on which Mo as a first metal component and a metal selected from among Co, Ni, W and combinations thereof as a second metal component are deposited, said first and said second metal component being contained in amounts from 10 to 30 wt% and from 2 to 10 wt%, respectively, based on total weight of the catalyst.

[Claim 9]

The process as defined in claim 8, wherein the hydrodesulfurization catalyst comprises a combination of CoMo and NiMo or of CoMo and NiW as catalytically active metal ingredients.

[Claim 10]

The process as defined in claim 8, wherein the support is made from gamma- alumina, silica, zeolite or combinations thereof.

[Claim 11 ]

The process as defined in claim 1, further comprising: reforming at least a part of the gasoil distillate having a boiling point exceeding the cut point separated in step a) by means of (i) selective hydrocracking; (ii) nitrogen adsorption/dewaxing/hydrodesulfurization; or (iii) hydrodesulfurization/dewaxing processes; and separating a diesel distillate from a stream obtained after the reforming step and pooling the diesel distillate with the light gasoil distillate obtained in step b).

[Claim 12]

The process as defined in claim 11, wherein step (i) is performed in conditions including a pressure of 40-120 kg/cm², a temperature of 340-410°C, a

1 "ϊ liquid hourly space velocity of 0.5-3.0 hr^' , and an H₂/oil ratio of 400-1500 Nm /kl.

[Claim 13]

The process as defined in claim 11, wherein step (ii) is performed in conditions including a pressure of 5-20 kg/cm², a temperature of 40~200°C, and a liquid hourly space velocity of 1.0-3.0 hr^"1 for the nitrogen adsorption, in conditions including a pressure of 30-80 kg/cm², a temperature of 300~410°C, a liquid hourly space velocity of 0.5-3.0 hr^'1, and an H₂/oil ratio of 200-1000 NnrVkl for the dewaxing, and in conditions including a pressure of 30-80 kg/cm², a temperature of 300~410°C, a liquid hourly space velocity of 0.5-3.0 hr^'1, and an H₂/oil ratio of 200-1 ,000 Nm³M for hydrodesulfurization.

[Claim 14]

The process as defined in claim 11, wherein the step (iii) is performed in conditions including a pressure of 30-80 kg/cm², a temperature of 300~410°C, a liquid hourly space velocity of 0.5-3.0 hr^" , and an H₂/oil ratio of 200-1000 Nm /kl for the hydrodesulfurization; and in conditions including a pressure of 30-80 kg/cm , a temperature of 300-410°C, a liquid hourly space velocity of 1.0-3.0 hr^"1, and an H₂/oil ratio of 200-1000 NπvVkl for the dewaxing.

[Claim 15]

The process as defined in claim 11, wherein the light gasoil distillate separated from the stream obtained after the reforming step has a sulfur level of 10 ppm or less and an aromatic level of 15 wt% or less.