US20090050524A1 - Method for producing feedstocks of high quality lube base oil from unconverted oil

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Abstract

Description

Claims

US20090050524A1

Publication number: US20090050524A1
Application number: US12/130,020
Authority: US
Inventors: Gyung Rok Kim; Chang Kuk Kim; In Chan Kim; Jee Sun Shin; Sam Ryong Park
Original assignee: SK Energy Co Ltd
Current assignee: SK Lubricants Co Ltd
Priority date: 2007-08-22
Filing date: 2008-05-30
Publication date: 2009-02-26
Also published as: KR101399207B1; KR20090020079A; MY169552A; JP2009046657A; JP5528681B2

The present invention relates to a method of producing a feedstock for high-quality lube base oil from unconverted oil (UCO) obtained from fuel oil hydrocracking, and more particularly to a method of producing a feedstock for high-quality lube base oil by treating vacuum gas oil (VGO) or a mixture of vacuum gas oil (VGO) with coker gas oil (CGO) or deasphalted oil (NAO) as a feedstock in a hydrotreating unit and a first hydrocracking unit and recycling the resulting unconverted oil (UCO) through a second hydrocracking unit.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No. 10-2007-0084507, filed Aug. 22, 2007, entitled “Method for producing feedstocks of high quality lube base oil from unconverted oil”, which is hereby incorporated by reference in its entirety into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a method of producing a feedstock for high-quality lube base oil from unconverted oil (UCO) obtained from fuel oil hydrocracking, and more particularly to a method of producing a feedstock for high-quality lube base oil by hydrotreating vacuum gas oil (VGO) or a mixture of vacuum gas oil (VGO) with coker gas oil (CGO) or deasphalted oil (DAO) as a feedstock in a hydrotreating unit and a first hydrocracking unit and recycling the resulting unconverted oil (UCO) through a second hydrocracking unit.
2. Description of the Prior Art
A process of producing a feedstock for high-quality lube base oil through a fuel oil hydrocracking process is a method of using unconverted oil (UCO), which is generated during the hydrocracking of vacuum gas oil (VGO) produced in a vacuum distillation unit (V1). In this method, the VGO is first fed into a hydrotreating (HDT) unit to remove sulfur, nitrogen, oxygen and metals from the VGO, and then a significant amount of the hydrotreated VGO is converted to light hydrocarbons through a hydrocracking (HDC) process, which is a main reaction process. The light hydrocarbons are passed through a series of fractionators (Fs) to separate various oils and gases therefrom, thus producing light oil products.
In the reaction, the pass conversion is generally designed to be about 40%, and it is impossible in practice to accomplish a pass conversion of 100%. For this reason, unconverted oil (UCO) is always generated in the fractionators, and a portion of the unconverted oil is drawn to the outside for use as a feedstock for lube base oil, and the remaining unconverted oil is recycled to the hydrocracking unit.
Aromatic compounds, sulfur compounds, oxygen compounds and nitrogen compounds, which are contained in the vacuum gas oil (VGO) feed in large amounts, are almost all saturated with hydrogen through the hydrotreating process. For this reason, more than 90% of the unconverted oil (UCO) byproducts are saturated hydrocarbons, and thus have a high viscosity index, which is one of the most important properties for lube base oil.
The applicant suggested an effective method of producing feedstocks for fuel oil and high-quality lube base oil, in which unconverted oil (UCO) is drawn out directly during the recycle mode operation of the vacuum gas oil (VGO) hydrocracking unit to provide a feedstock for producing lube base oil, such that the loads on a first vacuum distillation unit (V1; a process for vacuum distillation of atmospheric residue) and hydrotreating and hydrocracking units (R1 and R2) are reduced without the need to recycle the VGO to the first vacuum distillation process (V1) (Korean Patent Publication No. 96-13606). In this method, 100N- and 150N-grade feedstocks for high-quality lube base oils could be produced at greatly reduced inefficiency, but the method was designed to use only vacuum gas oil (VGO), and did not consider producing a feedstock for high-quality lube base oil in a more economic manner by recycling unconverted oil (UCO) using, in addition to vacuum gas oil, coker gas oil (CGO) or deasphalted oil (DAO), which are inexpensive and, at the same time, have a high concentration of impurities and low oxidation stability. Also, the method had shortcomings in that, because the hydrocracking unit consisted simply of a single stage, the size of the required reactor was increased, and in addition, the operating cost was increased due to the severity of operating conditions.

SUMMARY OF THE INVENTION

Accordingly, the applicant has conducted many studies to maximize the efficiency and economy of the above-described method for producing a feedstock for high-quality lube base oil and, as a result, has developed a method capable of effectively producing a feedstock for high-quality lube base oil by recycling unconverted oil, generated from the hydrotreating and hydrocracking of either vacuum gas oil or a mixture of vacuum gas oil with coker gas oil (CGO) or deasphalted oil (DAO), through a second hydrocracking process.
Therefore, the present invention provides a method for producing a feedstock for high-quality lube base oil, which can maximize efficiency by recycling unconverted oil (UCO) of an oil hydrocracking unit through a second hydrocracking unit and, at the same time, can remarkably improve economic efficiency by employing coker gas oil (CGO) or deasphalted oil (DAO), which is otherwise not very useful.
In one aspect, the present invention provides a method of producing a feedstock for high-quality lube base oil from unconverted oil, the method including: distilling atmospheric residue (AR) in a first vacuum distillation unit (V1) to obtain vacuum gas oil (VGO), and feeding the vacuum gas oil (VGO) into a hydrotreating unit (HDT); removing impurities from the vacuum gas oil through the hydrotreating unit (HDT); obtaining light and heavy hydrocarbons from the vacuum gas oil through a first hydrocracking unit (HDC1); feeding the light and heavy hydrocarbons into fractionators (Fs) to separate the hydrocarbons into oil products and unconverted oil; feeding a portion of the separated unconverted oil into a second vacuum distillation unit (V2) to obtain a feedstock for high-quality lube base oil, having a given viscosity grade, and the remaining unconverted oil; feeding the remaining unconverted oil, separated from the fractionators (Fs), and the unconverted oil, obtained from the second vacuum distillation unit (V2), into a second hydrocracking unit (HDC2); and recycling light and heavy hydrocarbons, obtained through the second hydrocracking process (HDC2), to the fractionators (Fs).
In another aspect, the present invention provides a method of producing a feedstock for high-quality lube base oil from unconverted oil, the method including: distilling atmospheric residue (AR) in a first vacuum distillation unit (V1) to separate it into vacuum gas oil (VGO) and vacuum residue (VR) or a mixture of atmospheric residue (AR) with vacuum residue (VR), feeding the vacuum gas oil (VGO) directly into a hydrotreating (HDT) unit, feeding the vacuum residue (VR) or the vacuum residue/atmospheric residue mixture (VR/AR) through fractionators (Fs) to coker drums to subject it to a coking process and passing the coked residue through fractionators (Fs′) to obtain coker gas oil, and feeding the obtained coker gas oil together with the vacuum gas oil (VGO) into a hydrotreating (HDT) unit; removing impurities from the vacuum gas oil and the coker gas oil through the hydrotreating (HDT) unit; obtaining light and heavy hydrocarbons from the vacuum gas oil through a first hydrocracking (HDC1) unit; feeding the light and heavy hydrocarbons into fractionators (Fs) to separate the hydrocarbons into oil products and unconverted oil; feeding a portion of the unconverted oil to a second vacuum distillation unit (V2) to obtain a feedstock for high-quality lube base oil, having a given viscosity grade, and the remaining unconverted oil; feeding the remaining unconverted oil, separated from the fractionators, and the unconverted oil, obtained from the second vacuum distillation unit (V2), into a second hydrocracking unit (HDC2); and recycling light and heavy hydrocarbons, obtained through the second hydrocracking unit (HDC2), to the fractionators.
In still another aspect, the present invention provides a method of producing a feedstock for high-quality lube base oil from unconverted oil, the method including: distilling atmospheric residue in a first vacuum distillation unit (V1) to separate it into vacuum gas oil (VGO) and vacuum residue (VR), feeding the vacuum gas oil (VGO) directly into a hydrotreating unit (HDT), feeding the vacuum residue into a solvent deasphalting unit (SDA) to obtain deasphalted oil (DAO) from which asphalt and impurities have been removed, and feeding the deasphalted oil (DAO) together with the vacuum gas oil (VGO) into the hydrotreating unit (HDT); removing impurities from the vacuum gas oil and the deasphalted oil through the hydrotreating unit (HDT); obtaining light and heavy hydrocarbons from the vacuum gas oil and the deasphalted oil through a first hydrocracking unit (HDC1); feeding the light and heavy hydrocarbons into fractionators (Fs) to separate the hydrocarbons into oil products and unconverted oil; feeding a portion of the separated unconverted oil to a second vacuum distillation unit (V2) to obtain a feedstock for high-quality lube base oil, having a given viscosity grade, and the remaining unconverted oil; feeding the remaining unconverted oil, separated from the fractionators, and the unconverted oil, obtained from the second vacuum distillation unit (V2), into a second hydrocracking unit (HDC2); and recycling light and heavy hydrocarbons, obtained through the second hydrocracking unit (HDC2), to the fractionators (Fs).
According to the present invention, the feedstock for high-quality lube base oil can be produced in a more efficient manner by carrying out the hydrotreating (HDT) process and the first hydrocracking (HDC1) process using vacuum gas oil (VGO) or the mixture of vacuum gas oil (VGO) with coker gas oil (CGO) or deasphalted oil (DAO) as a feedstock, and recycling the unconverted oil, obtained from the first hydrocracking unit, to the second hydrocracking unit (HDC2). Also, a high-value-added feedstock for high-quality lube base oil can be produced in a more economical manner through the use of coker gas oil (CGO) and deasphalted oil (DAO), which have a low grade and are difficult to treat.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic process diagram of an embodiment of the present invention, in which a feedstock for high-quality lube base oil is produced in a fuel oil hydrocracking process in a recycle-mode operation using vacuum gas oil as a feedstock;

FIG. 2 is a schematic process diagram of an embodiment of the present invention, in which a feedstock for high-quality lube base oil is produced in a fuel oil hydrocracking process in a recycle-mode operation using a mixture of vacuum gas oil and coker gas oil as a feedstock; and

FIG. 3 is a schematic process diagram of an embodiment of the present invention, in which a feedstock for high-quality lube base oil is produced in a fuel oil hydrocracking process in a recycle-mode operation using a mixture of vacuum gas oil and deasphalted oil as a feedstock.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic process diagram of an embodiment of the present invention, in which a feedstock for high-quality lube base oil is produced in a fuel oil hydrocracking process in a recycle-mode operation using vacuum gas oil (VGO) as a feedstock. As shown in FIG. 1, vacuum gas oil (VGO) produced from a first vacuum distillation unit (V1) is fed into a hydrotreating unit (HDT) to remove impurities, including sulfur, nitrogen, oxygen and metal components, from the vacuum gas oil (VGO), and a light oil fraction is produced from the hydrotreated vacuum gas oil through a first hydrocracking unit (HDC1). Also, unconverted oil (UCO), obtained from the first hydrocracking unit (HDC1), is fed into a second hydrocracking unit (HDC2) and recycled, thus producing a feedstock for high-quality lube base oil.
Unlike the prior single-stage hydrocracking process, in the present invention, the unconverted oil, obtained by passing the vacuum gas oil through the single-stage hydrotreating unit (HDT) and the first hydrocracking unit (HDC) and then passing the hydrocracked vacuum gas oil through fractionators (Fs), is fed into a second vacuum distillation unit (V2) to obtain a feedstock for high-quality lube base oil and the remaining amount of unconverted oil. The remaining amount of unconverted oil, obtained from the second vacuum distillation unit (V2), is introduced into a second hydrocracking unit (HDC2) to additionally produce diesel and light oil fractions, and then the produced diesel and light oil fractions are recycled to the fractionators (Fs).
In the two-stage hydrocracking process (HDC1 and HDC2) according to the present invention, hydrocracking is carried out in two separate reactors, unlike the prior hydrocracking unit, which consists only of a single stage. Thus, there are advantages in that the size of the reactors can be reduced, severity of operating conditions can be reduced, and the hydrocracking reaction can be easily controlled so as to maximize the production of diesel oil.
In general, because a one-through two-stage hydrocracking process is operated at a low conversion rate, the content of polycyclic aromatic components in the unconverted oil (UCO), which is a bottom oil fraction, is high, and the quality of the unconverted oil (UCO) is generally inferior to that in the case in which the single-stage hydrocracking process is used. For this reason, there is a problem in that the unconverted oil is difficult to use as a feedstock for high-quality lube base oil. However, in the present invention, the recovery of the required raw materials can be maximized by recycling the unconverted oil (UCO) through the two-stage hydrocracking process, and the reaction conversion rate can be increased by recycling the remaining unconverted oil (UCO), thus improving the quality of the feedstock for high-quality lube base oil. Also, the production of the feedstock for high-quality lube base oil can be increased.
The hydrotreating process (HDT) is a process of removing sulfur, nitrogen, oxygen and metal components from the vacuum gas oil as a feedstock, and the hydrotreated vacuum gas oil is converted to light hydrocarbons through a hydrocracking process in the first hydrocracking unit (HDC1).
The light and heavy hydrocarbons, produced through the first hydrocracking unit (HDC1), are fed into fractionators Fs to separate them into oil products and unconverted oil (UCO). A portion of the separated unconverted oil (UCO) is fed into a second vacuum distillation unit (V2) to separate a feedstock for high-quality lube base oil, having a given viscosity grade, therefrom, and to recover the remaining amount of unconverted oil (UCO).
The remaining amount of unconverted oil from the second vacuum distillation unit V2 is fed into a second hydrocracking unit (HDC2) together with the remaining unconverted oil resulting from the fractionators (Fs), and the light and heavy hydrocarbons produced through the second hydrocracking unit (HDC2) are recycled to the fractionators (Fs).
Herein, the ratio of the unconverted oil fed into the second hydrocracking unit (HDC2) to the unconverted oil produced in the fractionators Fs is preferably 1:2-1:5, and the ratio of the unconverted oil fed from the second vacuum distillation unit (V2) into the second hydrocracking unit (HDC2) to the unconverted oil fed into the second vacuum distillation unit (V2) is preferably 1:1.2-1:1.5.
The second vacuum distillation unit (V2) is operated at a bottom temperature of 320-350° C., a bottom pressure of 140-160 mmHg, a top temperature of 75-95° C. and a top pressure of 60-80 mmHg. The feedstock for high-quality lube base oil having a given viscosity grade, obtained in the second vacuum distillation unit (V2), can further be subjected to a dewaxing process and a stabilization process.
FIG. 2 is a schematic process diagram of an embodiment of the present invention, in which a feedstock for high-quality lube base oil is produced in a fuel oil hydrocracking process in a recycle-mode operation using a mixture of vacuum gas oil and coker gas oil as a feedstock. Referring to FIG. 2, in the present invention, atmospheric residue (AR), separated from a crude distillation unit (CDU), is distilled in a first distillation unit V1 to separate it into vacuum gas oil and vacuum residue or a mixture (VR/AR) of vacuum residue (VR) and atmospheric residue (AR). The vacuum gas oil (VGO) is fed directly to a hydrotreating unit HDT, and the vacuum residue (VR) or the atmospheric residue/vacuum residue mixture (VR/AR) is passed through fractionators (Fs′), subjected to a coking process in coker drums, and then passed again through the fractionators Fs′, thus obtaining coker gas oil (CGO). The coker gas oil (CGO) thus obtained is fed into a hydrocracking unit HDT together with the vacuum gas oil (VGO), and the two-stage hydrocracking process according to the present invention is carried out.
The process of producing the coker gas oil (CGO) will not be described in further detail. The vacuum residue (VR) or the atmospheric oil/vacuum residue mixture (VR/AR), separated from the first distillation unit (V1), is passed through the fractionators (Fs′) to separate low-boiling-point components therefrom, and the remaining oil fraction is fed into coker drums and heated in the coker drums to a temperature sufficient for forming coke. At this time, steam is also fed into the coker drums in order to maintain the lowest speed and the shortest residence time in the heater coils and to suppress the formation of coke in the heater coils. Liquid remaining in the coker drums is converted to coke and light hydrocarbon gases, and all of the gases are discharged through the top of the coker drums. In order to carry out this process, at least two coker drums are required. While coke is formed in one drum, the flow of oil to the other drum is blocked, and coke is removed from the other drum. The coker gas oil (CGO), produced through this coking process, has poor color stability and a high content of HPNA (heavy poly-nuclear aromatic hydrocarbons) (having more than 7 aromatic rings), and for this reason, unconverted oil (UCO), produced by feeding the coker gas oil to the hydrotreating and hydrocracking units, is unsuitable for use as a feedstock for high-quality lube base oil.
However, where unconverted oil (UCO) is recycled through the second hydrocracking unit (HDC2) according to the method of the present invention, it is possible to secure high-quality unconverted oil (UCO) having a low HPNA content and ensured stability, and the production of 100N- and 150N-grade feedstocks for high-quality lube base oil can be maximized. In addition, coker gas oil (CGO), which has been used as Bunker-C (B-C) oil or DSL oil, can be used as a raw material for producing high-quality lube base oil, and thus the added value of the product can be increased, leading to an improvement in economic efficiency.
Specific conditions for the coking process in the method according to the present invention are shown in Table 1 below.

	TABLE 1

	Operating conditions (unit)	Range

	Heater discharge temperature (° C.)	480-500
	Coker drum temperature (° C.)	500-600
	Top-coker drum pressure (psig)	15-30
	Recycling ratio, recycle volume/feed volume	0.05-0.2

The coker gas oil (CGO), produced from the coking process, is mixed with vacuum gas oil and fed into the hydrotreating unit HDT. When the content of the vacuum gas oil in the mixture of the coker gas oil (CGO) with the vacuum gas oil (VGO) is increased, the production of a feedstock for high-quality lube base oil will be increased, but the production cost will be increased, and when the content of the coker gas oil (CGO) is increased, the production cost will be advantageously reduced. However, because the properties of the coker gas oil (CGO) are inferior to those of the vacuum gas oil (VGO), the mixing volume ratio (VGO/CGO) between the vacuum gas oil (VGO) and the coker gas oil (CGO) is preferably 2-9.
The coker gas oil (CGO), extracted from the vacuum residue (VR) or the atmospheric residue/vacuum residue mixture (VR/AR) in an amount of about 20-50 vol %, can be mixed with the vacuum gas oil (VGO) and can be used as a feedstock in the hydrotreating and hydrocracking units (HDT and HDC). Thus, when the same amount of atmospheric residue (AR) is fed into the first distillation unit (V1), there is an advantage in that about 10-50% of the atmospheric residue can be converted to high-value-added light oil and a feedstock for high-quality lube base oil, unlike the case where only vacuum gas oil (VGO) is used as the feedstock in the first distillation unit (V1).
FIG. 3 is a schematic process diagram of an embodiment of the present invention, in which a feedstock for high-quality lube base oil is produced in a fuel oil hydrocracking process in a recycle-mode operation using a mixture of vacuum gas oil and deasphalted oil as a feedstock. Referring to FIG. 3, according to the present invention, atmospheric residue (AR) is distilled in a first vacuum distillation unit V1 to separate it into vacuum gas oil (VGO) and vacuum residue (VR). The vacuum gas oil (VGO) is fed directly to a hydrotreating unit HDT, and the vacuum residue (VR) is fed into a solvent deasphalting unit (SDA) to obtain deasphalted oil from which asphalt and impurities have been removed. The deasphalted oil (DAO) thus obtained is fed into the hydrotreating unit (HDT) together with the vacuum gas oil (VGO), and the two-stage hydrocracking reaction is carried out in the same manner as described above.
The process of producing the deasphalted oil (DAO) will now be described in further detail. The deasphalted oil (DAO) is produced by feeding the vacuum residue (VR), produced in the first vacuum distillation unit (V1), as a feedstock to the solvent deasphalting unit (SDA) so as to suitably remove asphalt and impurities therefrom. As the solvent in the solvent deasphalting unit (SDA), n- or iso-paraffin solvent having 3-6 carbon atoms is mainly used. Specifically, the solvent is selected from the group consisting of n-propane, n-butane, isobutene, n-pentane and n-hexane. Also, the yield of the deasphalted oil (DAO) with respect to the feedstock vacuum residue (VR) varies depending on the operating conditions and the kind of solvent, shows a tendency to increase with an increase in the carbon number of the solvent, and is generally about 15-80%.
The deasphalted oil (DAO), produced in the solvent deasphalting process, has low metal and residual carbon content, but has a high aromatic content and contains an oil fraction having a high boiling point, and thus it is difficult to use as a feedstock for high-quality lube base oil.
However, when the unconverted oil (UCO) is fed into the second hydrocracking unit (HDC2) and recycled according to the method of the present invention, the aromatic content of the deasphalted oil can be reduced, and it is possible to remove the oil fraction having high boiling point, and thus the deasphalted oil can be used as a feedstock for high-quality lube base oil. The use of such deasphalted oil (DAO) allows restriction on a feedstock for high-quality lube base oil to be relieved and the added value of the product to be increased, leading to an improvement in economic efficiency.
The deasphalted oil (DAO), extracted from the vacuum residue (VR) or the atmospheric residue/vacuum residue mixture (VR/AR) in an amount of about 20-50 vol %, can be mixed with the vacuum gas oil (VGO) and can be used as a feedstock in the hydrotreating and hydrocracking units (HDT and HDC). Thus, when the same amount of atmospheric residue (AR) is fed into the first distillation unit (V1), there is an advantage in that about 10-50% of the atmospheric residue can be converted to high-valued-added light oil and a feedstock for high-quality lube base oil, unlike the case where only vacuum gas oil (VGO) is used as the feedstock in the first distillation unit (V1).
When the content of the vacuum gas oil in the mixture of the deasphalted oil (DAO) with the vacuum gas oil (VGO) is increased, the production of high-quality lube base oil will be increased, but the production cost will be increased, and when the content of the deasphalted oil (DAO) is increased, the production cost will be advantageously reduced. However, because the properties of the deasphalted oil are inferior to those of the vacuum gas oil (VGO), the mixing volume ratio (VGO/DAO) between the vacuum gas oil (VGO) and the deasphalted oil (DAO) is preferably 2-9.
The typical properties of vacuum gas oil (VGO), coker gas oil (CGO) and deasphalted oil (DAO), which are fed into the hydrocracking unit (HDT) according to the present invention, are shown in Table 2 below.

	TABLE 2

	Properties of feedstocks
	in hydrocracking unit

	VGO	CGO	DAO

Specific gravity	0.8660	0.8504	0.8686
Sulfur/nitrogen (wt ppm)	937/750	1137/1614	2200/600
C7 insoluble substances (wt %)	0.35	0.05	0.01
Fe (wt ppm)	1.1	1.0	1.4
Ni + V (wt ppm)	1.0	1.0	LT 1.0
Si (wt ppm)	—	3.5	LT 1.0
Distillation (ASTM D-86)
Initial boiling point	324.8	207.0	266
5%	354.3	249.2	33.9
10%	373.6	272.2	348
30%	412.0	314.5	438
50%	440.7	342.5	488
70%	474.5	370.8	539
90%	529.6	405.5	604
95%	546.8	422.0	633
Final boiling point	586.0	452.0	699

Hereinafter, the present invention will be described in further detail with reference to examples, but the scope of the present invention is not limited thereto.

EXAMPLE 1

Vacuum gas oil (VGO), separated from atmospheric residue (AR) as a feedstock in the first vacuum distillation unit (V1), had the properties shown in Table 2 above, and was hydrotreated in the hydrotreating unit (HDT) under conditions of an LHSV (Liquid Hourly Space Velocity) of 3.881 hr⁻¹, a pressure of 2417 psig, a temperature of 389° C. and a hydrogen feed rate of 1374 Nm³/m³using KF-848 (Albemarle) as a catalyst. The hydrotreated oil was treated in the first hydrocracking unit (HDC1) under conditions of an LHSV of 1.068 hr⁻¹, a pressure of 170 bar and a temperature of 395° C. using DHC-8 (UOP) as a catalyst at a hydrogen feed rate of 1050 nm³/m³, and was then passed through a conventional separator and a plurality of fractionators to recover some of the diesel and light oil products, having a boiling point of less than 410° C. Then, the remaining oil was treated in the second hydrocracking unit (HDC2) together with the recycled UCO, described below, under conditions of an LHSV of 1.613 hr⁻¹, a pressure of 170 bar and a temperature of 403° C. using a DHC-8 catalyst (UOP) at a hydrogen feed rate of 1028 nm³/m³. Then, the hydrocracked oil was passed through a conventional separator and a plurality of fractionators to recover diesel and light oil products, having a boiling point of 410° C., thus obtaining unconverted oil (UCO) having the properties shown in Table 2 above. The obtained unconverted oil was subjected to vacuum distillation in a UCO vacuum distillation unit (V2) under conditions of a top pressure of 75 mmHg, a top temperature of 80° C., a bottom pressure of 150 mmHg and a bottom temperature of 325° C., thus obtaining 20 LV % light distillate, a 32 LV % 100N distillate, 22 LV % middle distillate, 4 LV % 150N distillate and 22 LV % bottom product, shown in Table 3 below.
Among them, only the 100N and 150N distillates were drawn out as intermediate products in an amount of 36% (100N: 32% and 150N: 4%) based on the feed amount (the amount of UCO fed into V2), and the remaining distillates (64% of the feed amount) were combined and recycled to the second hydrocracking unit (HDC2). Thus, 100N- and 150N-grade feedstocks for high-quality lube base oil, having a high viscosity index and 150N and low volatility, as shown in Table 3 below, were produced. Also, because 36% of UCO was drawn out, the accumulation of refractory components and poly-nuclear aromatic components were prevented, while the reaction conversion rate was increased, leading to an improvement in quality. In addition, the spare capacities of V1 and R1 were provided, and thus additional treatment capacity corresponding to the production of the feedstock for lube base oil was provided, and thus it was possible to use the system at very high efficiency.

TABLE 3

		100N	Middle	150N	Bottom
UCO	Light distillate	distillate	distillate	distillate	product

Specific gravity

0.8289

0.7393

0.8223

0.8287

0.8349

0.8421

Distillation, ASTM D1160, @760 mmHg, ° C.

Initial boiling point	220	227	368	387	406	412
5%	385	380	390	401	428	440
10%	404	395	402	421	440	465
30%	426	402	424	444	467	478
50%	450	410	438	459	482	496
70%	477	418	453	478	501	518
90%	535	426	471	503	521	541
95%	574	433	480	512	542	578
Final boiling point	613	446	495	533	573	613
Viscosity, cSt
@40° C.	13.15		17.74
@ 100° C.	3.493	2.968	4.226	5.065	6.653	7.523
Viscosity index	152	113	149	—	—	—
Flash point (COC) ° C.	146		230	243	266	289
Pour point	46		33	39	45	51

EXAMPLE 2

Vacuum residue (VR), separated from atmospheric residue (AR) as a feedstock in the first vacuum distillation unit (V1), was passed through the fractionators (Fs′) to separate some components having a low boiling point, and the remaining oil was heated to 500° C. and fed into coker drums. In the coker drums, the vacuum residue was heated under conditions of a temperature of 550° C. and a top coker drum pressure of 25 psig, so that liquid remaining in the drums was converted to coke and light hydrocarbon gases, and all of the gases were passed through the fractionators (Fs′) to separate them into LPG, gas, naphtha and coker gas oil (CGO).
The coker gas oil (CGO) and the vacuum gas oil (VGO) had the properties shown in Table 2, below, and were hydrocracked in the hydrocracking unit (HDT) under conditions of an LHSV of 3.56 hr⁻¹, a pressure of 2417 psig, a temperature of 384° C. and a hydrogen feed rate of 962 Nm³/m³using UF-210STARS (UOP) as a catalyst. The hydrocracked oil was treated in the first hydrocracking unit (HDC1) under conditions of an LHSV (Liquid Hourly Space Velocity) of 1.246 hr⁻¹, a pressure of 170 bar and a temperature of 395° C. using UF-210STARS/DHC-32 (UOP) as a catalyst at a hydrogen feed rate of 1180 Nm³/m³, and then was passed through a conventional separator and a plurality of fractionators to recover some diesel and light oil products having a boiling point lower than 370° C. The hydrocracked oil was treated in the second hydrocracking unit (HDC2) together with the recycled UCO, described below, in conditions of an LHSV of 1.613 hr⁻¹, a pressure of 170 bar and a temperature of 398° C. using a DHC-8 catalyst (UOP) at a hydrogen feed rate of 1028 Nm³/m³. Then, the hydrocracked oil was passed through a conventional separator and a plurality of fractionators to recover diesel and light oil products, having a boiling point lower than 370° C., thus obtaining unconverted oil (UCO) shown in Table 4 below. The obtained UCO was subjected to vacuum distillation in the second vacuum distillation unit (V2) under conditions of a top pressure of 75 mmHg, a top temperature of 80° C., a bottom pressure of 148 mmHg and a bottom temperature of 330° C., thus obtaining 30 LV % light distillate, 35 LV % 100N distillate, 18 LV % middle distillate, 4 LV % 150N distillate and 13 LV % bottom product, as shown in Table 4 below.
Among them, only the 100N and 150N distillates were drawn out as intermediate products in an amount of 39% (that is, 100N: 35% and 150N: 4%) based on the feed amount (the amount of UCO fed into V2), and the remaining distillates (61%) were combined and recycled to the second hydrocracking unit (HDC2). Thus, 100N- and 150N-grade feedstocks for high-quality lube base oil, having high viscosity index and low volatility, as shown in Table 4, were produced, and because 39% of the UCO was drawn out, high-quality unconverted oil, having a low poly-nuclear aromatic component content and ensured stability, could be secured. Also, because additional treatment capacity corresponding to the production of the feedstock for lube base oil was provided, the system could be very efficiently utilized. In addition, because coker gas oil (CGO), which has been used B-C oil or DSL oil, could be used as a raw material for producing high-quality lube base oil, the added value of the feedstock could be increased, leading to an improvement in economic efficiency.

TABLE 4

	Light	100N	Middle	150N	Bottom
UCO	distillate	distillate	distillate	distillate	product

Specific gravity

0.8250

0.7390

0.8223

0.8284

0.8348

0.8423

Distillation, ASTM D1160, @760 mmHg, ° C.

Initial boiling point	225	227	365	381	403	410
5%	372	368	388	400	426	440
10%	395	384	400	421	438	465
30%	416	402	422	444	466	478
50%	442	408	436	456	482	498
70%	471	416	452	477	503	518
90%	530	424	470	498	521	539
95%	572	431	479	510	543	579
Final boiling point	613	444	494	531	574	613
Viscosity, cSt
@40° C.	12.9		17.62
@ 100° C.	3.432	2.932	4.21	5.060	6.652	7.526
Viscosity index	149	112	148
Flash point (COC) ° C.	142		222	240	264	286
Pour point	42		33	39	45	51

EXAMPLE 3

Vacuum residue (VR), separated from atmospheric residue (AR) as a feedstock in the first vacuum distillation unit (V1), was fed into the solvent deasphalting unit (SDA) to suitably remove asphalt and impurities therefrom. Herein, as the deasphalting solvent, n-propane (N-C3) was used, and the deasphalted oil (DAO) was produced at a yield of 39% at a pressure of 45.7 kg/cm²g and an asphaltene separation temperature of 83° C. The vacuum gas oil (VGO) and the deasphalted oil (DAO), having the properties shown in Table 2 above, were fed into the hydrotreating unit (HDT) at a mixing volume ratio (VGO/DAO) of 3-5 and hydrocracked therein under conditions of an LHSV of 3.01 hr⁻¹, a pressure of 2488 psig, a temperature of 395° C. and a hydrogen feed rate of 1125 Nm³/m³using UF-210STARS (UOP) as a catalyst. The hydrotreated oil was treated in the first hydrocracking unit (HDC1) under conditions of an LHSV (Liquid Hourly Space Velocity) of a 1.208 hr⁻¹, pressure of a 170 bar and temperature of a 405° C. using UF-210STARS/DHC-32 (UOP) as a catalyst at a hydrogen feed rate of 1250 Nm³/m³, and then passed through a conventional separator and a plurality of fractionators to recover some of diesel and light oil products, having a boiling temperature of 370° C. The hydrocracked oil was treated in the second hydrocracking unit (HDC2) together with the recycled UCO, described below, under conditions of an LHSV of 1.405 hr⁻¹, a pressure of 170 bar and a temperature of 403° C. using a HC-215 catalyst (UOP) at a hydrogen feed rate of 1200 Nm³/m³. Then, the hydrocracked oil was passed through a conventional separator and a plurality of fractionators to recover diesel and light oil products, having a boiling point lower than 370° C., thus obtaining unconverted oil (UCO) having the properties shown in Table 5 below. The unconverted oil was fed into the vacuum distillation unit (V2), in which it was subjected to vacuum distillation under conditions of a top pressure of 70 mmHg, a top temperature of 80° C., a bottom pressure of 150 mmHg and a bottom temperature of 345° C., thus obtaining 17 LV % light distillate, 30 LV % 100N distillate, 20 LV % middle distillate, 4 LV % 150N distillate and 29 LV % bottom product.
Among them, only the 100N and 150N distillates were drawn out as intermediate products in an amount of 34% (that is, 100N: 30% and 150N: 4%) based on the feed amount (the amount of UCO fed into V2), and the remaining distillates (66%) were combined and recycled to the second hydrocracking unit (HDC2). Thus, the 100N- and 150N-grade feedstocks for high-quality lube base oil, having high viscosity index and low volatility, as shown in Table 5 below, were produced. Also, because 34% of the UCO was drawn out, oil fractions, having a low poly-nuclear aromatic component content and a high boiling point, could be removed, so that high-quality unconverted oil could be secured, and restriction on feedstock oil was relieved, and thus the added value of the product could be increased, leading to an improvement in economic efficiency.

TABLE 5

				150N	Bottom
UCO	Light distillate	100N distillate	Middle distillate	distillate	product

Specific gravity

0.8340

0.7390

0.8223

0.8284

0.8348

0.8423

Distillation, ASTM D1160, @760 mmHg, ° C.

Initial boiling point	225	227	365	381	403	410
5%	372	368	388	400	427	450
10%	395	384	400	421	443	472
30%	416	402	422	443	470	494
50%	458	408	436	455	493	518
70%	529	413	452	476	510	549
90%	562	420	470	497	530	595
95%	598	428	479	508	558	613
Final boiling point	699	440	494	529	589	699
Viscosity, cSt
@40° C.	12.9		17.62
@ 100° C.	3.432	2.918	4.21	5.05	6.80	9.082
Viscosity index	149	109	146	—	—	—
Flash point (COC) ° C.	142		220	239	264	301
Pour point	42		33	39	45	53

COMPARATIVE EXAMPLE

Vacuum gas oil (VGO), separated from atmospheric residue (AR) as a feedstock in the first vacuum distillation unit and having the properties shown in Table 2, was treated in a hydrotreating unit under conditions of an LHSV (Liquid Hourly Space Velocity) of 3.429 hr⁻¹, a pressure of 2397 psig and a temperature of 385.8° C. using UF-210STARS (UOP) as a catalyst at a hydrogen feed rate of 842 Nm³/m³. The hydrotreated oil was treated in a hydrocracking unit together with the recycled UCO, described below, under conditions of an LHSV of 1.241 hr⁻¹, a pressure of 2397 psig and a temperature of 395.2° C. using a UF-210/HC-115/UF-100 catalyst (UOP) at a hydrogen feed rate of 1180 Nm³/m³.
Then, the hydrocracked oil was passed through a conventional separator and a plurality of fractionators to recover diesel and light oil products, having a boiling point lower than 350° C., thus obtaining unconverted oil (UCO) having the properties shown in Table 6. The unconverted oil was fed into a second vacuum distillation unit and subjected to vacuum distillation therein under conditions of a top pressure of 75 mmHg, a top temperature of 80° C., a bottom pressure of 150 mmHg and a bottom temperature of 325° C., thus obtaining 32.5 LV % light distillate, 34.8 LV % 100N distillate, 14.6 LV % middle product distillate and 18.1 LV % bottom product 150N distillate.
Among them, only the 100N and 150N distillates were drawn out as intermediate products in an amount of 52.9% (that is, 100N: 34.8% and 150N: 18.1%) based on the feed amount (the amount of the UCO fed into the second vacuum distillation unit), and the remaining distillates (47.1% of the feed amount) were combined and recycled to a hydrocracking process. Thus, the 100N- and 150N-grade feedstocks for high-quality lube base oil, having high viscosity indexes and low volatilities, as shown in Table 6 below, were produced.

Specific gravity

0.8271

0.8374

0.8388

0.8418

0.8449

Distillation, ASTM D1160, @760 mmHg, ° C.

Initial boiling point	276	338	401	412	437
5%	368	358	410	428	449
10%	398	362	412	434	453
30%	432	376	418	443	461
50%	457	383	424	459	475
70%	485	392	432	478	496
90%	537	403	447	503	531
95%	567	406	456	532	552
Final boiling point	590	414	471	533	562
Viscosity, cSt
@40° C.	20		19.39
@ 100° C.	4.428	2.978	4.305	5.056	6.787
Viscosity index	136	113	132	—	—
Flash point (COC) ° C.			212		250
Pour point			33		39

Although the preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Light distillate

100N distillate

distillate

distillate

1. A method of producing a feedstock for high-quality lube base oil from unconverted oil, the method comprising:

distilling atmospheric residue (AR) in a first vacuum distillation process (V1) to obtain vacuum gas oil (VGO), and feeding the vacuum gas oil (VGO) into a hydrotreating unit (HDT);

removing impurities from the vacuum gas oil through the hydrotreating unit (HDT);

obtaining light and heavy hydrocarbons from the vacuum gas oil through a first hydrocracking unit (HDC1);

feeding the light and heavy hydrocarbons into fractionators (Fs) to separate the hydrocarbons into oil products and unconverted oil;

feeding a portion of the separated unconverted oil into a second vacuum distillation unit (V2) to obtain a feedstock for high-quality lube base oil, having a given viscosity grade, and the remaining unconverted oil;

feeding the remaining unconverted oil separated from the fractionators (Fs) and the unconverted oil obtained from the second vacuum distillation unit (V2) into a second hydrocracking unit (HDC2); and

recycling light and heavy hydrocarbons, obtained through the second hydrocracking process (HDC2), to the fractionators (Fs).

2. A method for producing a feedstock for high-quality lube base oil from unconverted oil, the method comprising:

distilling atmospheric residue (AR) in a first vacuum distillation process (V1) to separate it into vacuum gas oil (VGO) and vacuum residue (VR) or a mixture of atmospheric residue (AR) with vacuum residue (VR), feeding the vacuum gas oil (VGO) directly into a hydrotreating (HDT) unit, feeding the vacuum residue (VR) or the vacuum residue/atmospheric residue mixture (VR/AR) through fractionators (Fs′) to coker drums to subject it to a coking process and passing the coked residue through fractionators (Fs′) to obtain coker gas oil, and feeding the obtained coker gas oil together with the vacuum gas oil (VGO) into a hydrotreating (HDT) unit;

removing impurities from the vacuum gas oil and the coker gas oil through the hydrotreating (HDT) unit;

obtaining light and heavy hydrocarbons from the vacuum gas oil through a first hydrocracking (HDC1) unit;

feeding a portion of the unconverted oil to a second vacuum distillation unit (V2) to obtain a feedstock for high-quality lube base oil, having a given viscosity grade, and the remaining unconverted oil;

feeding the remaining unconverted oil, separated from the fractionators, and the unconverted oil, obtained from the second vacuum distillation unit (V2), into a second hydrocracking unit (HDC2); and

recycling light and heavy hydrocarbons, obtained through the second hydrocracking unit (HDC2), to the fractionators (Fs).

3. A feedstock of producing a feedstock for high-quality lube base oil from unconverted oil, the method comprising:

distilling atmospheric residue in a first vacuum distillation unit (V1) to separate it into vacuum gas oil (VGO) and vacuum residue (VR), feeding the vacuum gas oil (VGO) directly into a hydrotreating unit (HDT), feeding the vacuum residue into a solvent deasphalting unit (SDA) to obtain deasphalted oil (DAO) from which asphalt and impurities have been removed, and feeding the deasphalted oil (DAO) together with the vacuum gas oil (VGO) into the hydrotreating unit (HDT);

removing impurities from the vacuum gas oil and the deasphalted oil through the hydrotreating unit (HDT);

obtaining light and heavy hydrocarbons from the vacuum gas oil and the deasphalted oil through a first hydrocracking unit (HDC1);

4. The method of claim 2, wherein the mixing volume ratio (VGO/CGO) between the vacuum gas oil (VGO) and the coker gas oil (CGO), which are fed into the hydrotreating unit (HDT), is 2-9.

5. The method of claim 3, wherein the mixing volume ratio (VGO/DAO) between the vacuum gas oil (VGO) and the deasphalted oil (DAO), which are fed into the hydrotreating unit (HDT), is 2-9.

6. The method of claim 1, wherein the ratio of the unconverted oil fed into the second hydrocracking unit HDC2 to the unconverted oil produced in the fractionators Fs is 1:2-1:5.

7. The method of claim 2, wherein the ratio of the unconverted oil fed into the second hydrocracking unit HDC2 to the unconverted oil produced in the fractionators Fs is 1:2-1:5.

8. The method of claim 3, wherein the ratio of the unconverted oil fed into the second hydrocracking unit HDC2 to the unconverted oil produced in the fractionators Fs is 1:2-1:5.

9. The method of claim 1, wherein the ratio of the unconverted oil fed from the second vacuum distillation unit (V2) into the second hydrocracking unit HDC2 to the unconverted oil fed into the second vacuum distillation unit V2 is 1:1.2-1:1.5.

10. The method of claim 2, wherein the ratio of the unconverted oil fed from the second vacuum distillation unit (V2) into the second hydrocracking unit HDC2 to the unconverted oil fed into the second vacuum distillation unit V2 is 1:1.2-1:1.5.

11. The method of claim 3, wherein the ratio of the unconverted oil fed from the second vacuum distillation unit (V2) into the second hydrocracking unit HDC2 to the unconverted oil fed into the second vacuum distillation unit V2 is 1:1.2-1:1.5.