EP4606877A1

EP4606877A1 - Method for producing recycled lubricating base oil from waste lubricating oil and recycled lubricating base oil produced thereby

Info

Publication number: EP4606877A1
Application number: EP25152306.4A
Authority: EP
Inventors: Yun Ha Kim; Jae Woo Oh; Min Gyun Suk
Original assignee: SK Innovation Co Ltd; SK Enmove Co Ltd
Current assignee: SK Innovation Co Ltd; SK On Co Ltd
Priority date: 2024-02-26
Filing date: 2025-01-16
Publication date: 2025-08-27
Also published as: US20250270467A1; JP2025130031A; CN120536159A; KR20250131111A

Abstract

The present disclosure relates to a method for producing a recycled lubricating base oil from waste lubricating oil. The method includes: a) first pretreating the waste lubricating oil, b) performing distillation to recover a fraction having a specific boiling point from the first pretreated waste lubricating oil, c) second pretreating the fraction recovered in step b), and d) hydroprocessing the second pretreated fraction in the presence of a catalyst. The recycled lubricating base oil produced by the above method has a viscosity index (VI) of equal to or greater than 130. The proposed method makes it possible to produce a high-grade lubricating base oil using only waste lubricating oil as a feed, thereby reducing the cost of raw materials for production of lubricating base oil, and having the advantage of being environmentally friendly.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method for producing a recycled lubricating base oil from waste lubricating oil and a recycled lubricating base oil produced thereby.

Description of the Related Art

The American Petroleum Institute (API) classifies mineral base oils derived from crude oil according saturation, sulfur content, and viscosity index (VI), as illustrated in Table 1 below.

Table 1

Group	Sulfur content (ppm)		Saturation (%)	Viscosity index (VI)
I	> 300	and/or	< 90	80-120
II	≤ 300	and	≥ 90	80-120
III	≤ 300		≥ 90	> 120
IV	All Polyalphaolefins(PAOs)
V	All stocks not in Group I-IV

Of these, base oils that meet all Group III criteria and have a viscosity index of equal to or greater than 130, although not included in the classification criteria, are classified as Group III+ base oils in terms of differentiation from existing Group III base oils with a viscosity index of equal to or greater than 120, and are usually traded at higher prices in the global market as they are considered to have superior performance compared to Group III base oils. Global environmental regulations and responses to them require improved fuel efficiency and energy efficiency using high-grade lubricating oils. Accordingly, demand for high-performance Group III+ base oils is expected to continue to increase.

SUMMARY OF THE INVENTION

The present invention has been made keeping in mind the above problems occurring in the related art, and one objective of the present invention is to provide a method for producing a recycled lubricating base oil having improved performance in terms of viscosity index.
In order to achieve the above objective, according to one aspect of the present invention, there is provided a method for producing a recycled lubricating base oil from waste lubricating oil, the method including: a) a first pretreating step of pretreating a waste lubricating oil; b) a distillation step of performing distillation to recover a fraction having a specific boiling point from the first pretreated waste lubricating oil recovered in step a); c) a second pretreating step of pretreating the fraction recovered in step b); and d) a hydroprocessing step of hydroprocessing the second pretreated fraction in the presence of a catalyst. The recycled lubricating base oil may have a viscosity index (VI) of equal to or greater than 130.
In one embodiment, the waste lubricating oil prior to step a) may have a viscosity index of equal to or less than 120, a sulfur content of equal to or greater than 10,000 ppm, and a nitrogen content of equal to or greater than 300 ppm.
In one embodiment, step a) may include coagulant addition, centrifugal separation, or a combination thereof.
In one embodiment, step b) may include atmospheric distillation, vacuum distillation, or a combination thereof.
In one embodiment, step b) may comprise atmospheric distillation, wherein the atmospheric distillation is preferably carried out at a temperature of 50°C to 350°C.
In one embodiment, step b) may comprises vacuum distillation, which is preferably carried out at a pressure of equal to or less than 10 torr, or a temperature of 150°C to 600°C, or both.
In one embodiment, step b) may comprise a combination and preferably a sequence of atmospheric distillation and vacuum distillation. Preferably, a fraction having a boiling point of equal to or greater than 150°C is collected from the atmospheric distillation and this fraction is then subjected to the vacuum distillation, which yields the fraction recovered in step b).
In one embodiment, the fraction recovered in step b) may have a boiling point of 300°C to 500°C.
In one embodiment, wherein step c) may include solvent extraction.
In one embodiment, the solvent used for the solvent extraction may include one or more of N-methyl-2-pyrrolidone (NMP), sulfolane, dimethylsulfoxide (DMSO), furfural, phenol, and acetone.
In one embodiment, the solvent extraction may be performed at a temperature of 60°C to 80°C, a solvent-oil ratio of 1.5:1 to 2.5:1 by volume, or both.
In one embodiment, in step d), a proportion of an unsupported catalyst in the catalyst may be 20% to 70% by volume, preferably 30% to 60% by volume, more preferably 40% to 50% by volume.
In one embodiment, the catalyst used in step d) may include a metal, and the metal may include Ni, W, Mo, Co, or a combination thereof, preferably in the form of an oxide.
In one embodiment, the method further includes the following step: e) a step of dewaxing and/or hydrofinishing the hydroprocessed fraction recovered in step d).
According to another aspect of the present invention, there is provided a recycled lubricating base oil having a sulfur content of equal to or less than 5 ppm, a saturation of equal to or greater than 90%, and a viscosity index (VI) of equal to or greater than 130. The recycled lubricating base oil is preferably obtained by a method of the present invention.
In one embodiment, the recycled lubricating base oil may have a kinematic viscosity of 4 to 5 cSt at 100°C and a pour point of equal to or less than -15°C.
According to the present invention, it is possible to produce a Group III lubricating base oil having an improved viscosity index in an environmentally friendly manner.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other obj ectives, features, and other advantages of the present invention will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a flowchart illustrating a method for producing a recycled lubricating base oil from waste lubricating oil according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term "recycled lubricating oil" refers to a lubricating base oil produced using only waste lubricating oil as a feed without mixing with a separate fraction such as unconverted oil (UCO) supplied from an external source.
According to the present invention, there is provided a method for producing a recycled lubricating base oil from waste lubricating oil is provided, the method including: a) a first pretreating step of pretreating a waste lubricating oil; b) a distillation step of performing distillation to recover a fraction having a specific boiling point from the first pretreated waste lubricating oil recovered in step a); c) a second pretreating step of pretreating the fraction recovered in step b); and d) a hydroprocessing step of hydroprocessing the second pretreated fraction recovered in step c) in the presence of a catalyst.
The first pretreating of the waste lubricating oil (step a)) is a step of reducing the content of impurities present in the waste lubricating oil. The content of impurities may be reduced in subsequent steps of the method for producing the recycled lubricating base oil according to the present invention. However, by reducing the content of impurities in the waste lubricating oil in advance in the pretreatment step, the burden on the subsequent steps may be reduced, and the content of impurities may be further reduced compared to when the first pretreatment is not performed.
In one embodiment, the waste lubricating oil prior to step a) may have a viscosity index of equal to or less than 120, a sulfur content of equal to or greater than 10,000 ppm, and a nitrogen content of equal to or greater than 300 ppm. As described above, waste lubricating oil including base oil belonging to Group I in the above API classification may also be used as a feed for the method for producing the recycled lubricating base oil according to the present invention, and may be converted into a Group III+ recycled base oil through a series of steps. This not only reduces the manufacturing cost of high-grade recycled base oils, but also has an advantage in terms of environmental friendliness by recycling waste lubricating oil that can no longer be recycled and needs to be discarded. Waste lubricating oil having a viscosity index greater than the above viscosity index and lower sulfur and nitrogen contents, i.e., waste lubricating oil including base oils belonging to Group II and Group III in the API classification, may also be used as a feed for the method for producing the recycled lubricating base oil according to the present invention.
In one embodiment, step a) may include coagulant addition, centrifugal separation, or a combination thereof. The coagulant addition is a process of coagulating sulfur, nitrogen, chlorine, and other impurities present in the waste lubricating oil to form aggregates and separating them from fractions by density differences. Any coagulant capable of coagulating impurities in waste lubricating oil may be used without limitation. For example, the coagulant to be added may be alum. The centrifugal separation is a process of separating and removing impurities present in the waste lubricating oil through precipitation, and may be performed at a rotation speed of about 100 to 3,000 rpm. Instead of the centrifugal separation, precipitation of impurities by natural sedimentation is also possible, but the centrifugal separation is more preferable from the perspective of separation speed and performance. The coagulant addition and the centrifugal separation may be performed in combination. Specifically, when the centrifugal separation is performed on the waste lubricating oil after the coagulant addition, the time required for formation of impurity aggregates may be shortened, and the formed impurity aggregates may be more completely removed by precipitation.
The method includes performing the distillation to recover the fraction having the specific boiling point from the first pretreated waste lubricating oil (step b)). Step b is a distillation step of obtaining a fraction having a desired viscosity index and kinematic viscosity from the waste lubricating oil. In the distillation step, fractions in the first pretreated waste lubricating oil are distilled and fractionated in order of lower boiling points as the atmospheric distillation temperature increases.
In one embodiment, step b) may include atmospheric distillation, vacuum distillation, or a combination thereof.
The atmospheric distillation is performed at a temperature of about 50°C to 350°C under atmospheric pressure. As the atmospheric distillation temperature increases, fractions in the waste lubricating oil are distilled and fractionated in order of lower boiling points. Among the fractions fractionated through the atmospheric distillation step, a fraction having a boiling point of about equal to or greater than 150°C is collected to produce a refined oil fraction.
The fraction collected in the atmospheric distillation step is then subjected to the vacuum distillation. The vacuum distillation is performed for further fractionation of the fraction obtained in the atmospheric distillation step. When the distillation temperature is increased for the fractionation of the fraction under atmospheric pressure, oil fraction cracking may occur. For this reason, this step is performed in reduced pressure and mild temperature conditions. The vacuum distillation may be performed at a pressure of equal to or less than 10 torr and a temperature of 150°C to 600°C. During the vacuum distillation step, a fraction having a boiling point of 300°C to 550°C is collected and is referred to as a refined oil fraction. The refined oil fraction has a kinematic viscosity of about 4 to 6 cSt at a temperature of 100°C, a viscosity index (VI) of about 90 to 123, and a pour point of about -20°C to 0°C. Additionally, the refined oil fraction may have a sulfur content of about 200 to 2,000 ppm, a nitrogen content of about 100 to 1,000 ppm, and a chlorine content of about 30 to 2,000 ppm. That is, the refined oil fraction may have a reduced impurity content compared to the first pretreated waste lubricating oil. The refined oil fraction shows a brown color of about 5 to 6 according to ASTM standards. By the centrifugal separation and two-step distillation, the refined oil fraction may have a sediment and moisture content that is significantly reduced compared to the waste lubricating oil prior to the pretreatment and distillation steps.
The method includes second pretreating the fraction recovered in the distillation step to remove impurities (step c)). The second pretreating is a step of additionally treating the fraction (refined oil fraction) recovered in the distillation step to minimize the influence of the refined oil fraction on the process and the catalyst before the refined oil fraction is subj ected to hydroprocessing.
In one embodiment, step c) may include solvent extraction. The solvent extraction is a step of blending the refined oil fraction and a solvent in a blending tank, allowing the mixture to settle to reach phase separation, thereby obtaining a phase in which oil is a main component, and removing a phase containing a large amount of impurities. The solvent used for the solvent extraction is a solvent having a higher affinity to impurities than the oil component in the refined oil fraction. Examples of the solvent include N-methyl-2-pyrrolidone (NMP), sulfolane, DMSO, furfural, phenol, and acetone. Since the solvent has a high affinity to impurities and a low affinity to the oil component in the refined oil fraction, the solvent is phase-separated from the oil component in the refined oil fraction. Any solvent may be used without limitation as long as it has a different volatility for the subsequent solvent separation step. In one embodiment, the solvent extraction may be performed in a batch or continuous process configuration, and may be performed at a temperature of about 60°C to 80°C, a solvent-oil ratio of about 1.5:1 to 2.5:1 by volume, and a stirring speed of about 400 to 700 rpm. Additionally, in order to reduce the impurity content in the refined oil fraction to a desired level, the layer containing a large amount of impurities located at the bottom after settling and phase separation may be removed, and the solvent extraction may be performed repeatedly by additionally adding a solvent. After the impurity content in the refined oil fraction is reduced to the desired level, water is added to the refined oil layer to phase-separate and remove a polar solvent.
The method includes hydroprocessing the second pretreated fraction in the presence of the catalyst (step d)). The hydroprocessing is a step of hydrogenating the second pretreated fraction at high temperature and high pressure in the presence of the catalyst to remove sulfur, nitrogen, and other metallic impurities contained in the fraction derived from the waste lubricating oil, and saturating unsaturated hydrocarbons present in the fraction derived from the waste lubricating oil. Through the hydroprocessing step, a recycled lubricating base oil is obtained. The obtained recycled lubricating base oil has an improved viscosity index compared to existing Group III lubricating oils, and exhibits a viscosity index of equal to or greater than 130.
In one embodiment, in step d), the proportion of an unsupported catalyst in the catalyst may be 20% to 70% by volume. Unlike conventional hydrocracking catalysts, unsupported catalysts without a separate support have a structural feature and configuration that suppress the cracking function and maximize the hydrogenation function that saturates unsaturated hydrocarbons, thereby having particular advantages in improving the viscosity index by removing impurities in the second pretreated fraction and increasing the paraffin content. When the proportion of the unsupported catalyst in the catalyst is less than 20%, the hydrogenation function of the catalyst may not be sufficient to achieve a viscosity index of equal to or greater than 130. When the proportion of the unsupported catalyst in the catalyst exceeds 70%, the metal content in the catalyst is inevitably high, which may be disadvantageous in terms of cost, and the cracking performance of the catalyst may low, so impurities in the fraction may not be removed efficiently. In one embodiment, the proportion of the unsupported catalyst in the catalyst may be specifically 30% to 60%, more specifically 40% to 50%.
In one embodiment, the catalyst may include a metal, and the metal may include Ni, W, Mo, Co, or a combination thereof. In the catalyst, the metal acts as an active site and promotes a hydrogenation reaction of a feed. More specifically, the metal included in the catalyst may be in the form of a metal oxide, and may be an oxide of Ni, W, Mo, and Co, which have excellent hydrogenation function among metal oxides. The metal may be included in the catalyst in combination, for example, Ni/W/Mo or Co/W/Mo.
In one embodiment, the method may further include performing dewaxing and performing hydrofinishing. The main reaction in the dewaxing step is isomerization, which converts N-paraffin to iso-paraffin to improve the low-temperature properties of the recycled lubricating base oil. For this reason, the dewaxing step may also be referred to as isodewaxing (IDW). The dewaxing may be performed in the presence of a zeolite-based precious metal catalyst.
The hydrofinishing is a step of allowing hydrogen gas and the recycled lubricating base oil to pass through a catalyst layer to remove trace amounts of impurities such as sulfur and nitrogen present in the recycled lubricating base oil as the final product. The catalyst layer may include an alumina-based precious metal catalyst. The hydrofinishing step may be performed at a temperature of about 200°C to 250°C and a liquid hourly space velocity (LHSV) of 0.5 to 2.0 h^-1.

Exemplary properties of a feed after each step of the method for producing the recycled lubricating base oil from the waste lubricating oil are as illustrated in Table 2 below.

Table 2

	Waste lubricating oil	Refined oil fraction	Solvent extraction	Hydrogenation	Lubricating base oil
Specific gravity	0.8 to 0.9	0.8 to 0.9	0.8 to 0.9	0.8 to 0.9	0.8 to 0.9
Kinematic viscosity (@ 100°C), cSt	2 to 20	4 to 6	4 to 6	4 to 5	4 to 5
Viscosity index	60 to 150	100 to 120	110 to 130	130 to 140	> 130
Pour point (°C)	-18 to -12	-18 to -3	-18 to -3	-18 to -3	Equal to or less than -15
Sulfur, ppm	1000 to 3000	200 to 1000	70 to 150	0 to 5	Equal to or less than 1
Nitrogen, ppm	500 to 2000	200 to 400	40 to 100	0 to 1	Equal to or less than 1
Chlorine, ppm	100 to 2000	30 to 2000	5 to 20	0 to 1	Equal to or less than 1
Aromatic compound, wt%	Equal to or greater than 10%	0 to 10	0 to 5	0 to 1	Equal to or less than 1

By the above method, a recycled lubricating base oil having a viscosity index (VI) of equal to or greater than 130 may be produced using only waste lubricating oil as a feed.
According to the present invention, there is provided a recycled lubricating base oil having a sulfur content of equal to or less than 5 ppm, a saturation of equal to or greater than 90%, and a viscosity index (VI) of equal to or greater than 130. The recycled lubricating base oil may be produced using only waste lubricating oil as a feed, according to the above method for producing the recycled lubricating base oil. The recycled lubricating base oil satisfies the conditions required for Group III in the API classification in terms of sulfur content and saturation, and its viscosity index is significantly greater than the Group III criteria, so it corresponds to the Group III+ lubricating base oil described above.
In one embodiment, the recycled lubricating base oil may have a kinematic viscosity of 4 to 5 cSt at 100°C and a pour point of equal to or less than -15°C. The recycled lubricating base oil has a viscosity required for Group III and Group III+ as described above, and has a low pour point so as to maintain fluidity even at low temperature, thereby exhibiting excellent performance as a lubricating base oil.
Hereinbelow, the embodiments of the present invention will be further described with reference to specific experimental examples.

Example - Confirmation of change in viscosity index of recycled lubricating base oil according to catalyst

Experimental Example

According to the flowchart illustrated in FIG. 1, alum was added as a coagulant to waste lubricating oil having a specific gravity of 0.8, a kinematic viscosity of 4 cSt at 100°C, a viscosity index of 100, a sulfur content of 2,500 ppm, a nitrogen content of 1,800 ppm, and a chlorine content of 1,500 ppm, and the mixture was allowed to pretreated (settled) for 30 minutes, thereby precipitating and removing aggregates of sulfur, nitrogen, chlorine, and other impurities in the waste lubricating oil. Thereafter, the pretreated waste lubricating oil was distilled (ADU) at a temperature of 50°C to 350°C under atmospheric pressure to collect a fraction having a boiling point of equal to or greater than 150°C. The collected fraction was subjected to vacuum distillation (VDU) at a pressure of 5 torr and a temperature of 150°C to 600°C. In this step, a fraction having a boiling point of 300°C to 550°C was collected. The fraction collected in the distillation step was subjected to solvent extraction using N-methyl-2-pyrrolidone (NMP) as a solvent. The solvent extraction was performed at atmospheric pressure and a temperature of ~ 70°C, with a solvent-oil ratio (SOR) of 1.5. The fraction with reduced impurity content by the solvent extraction was subjected to hydroprocessing in a reactor loaded with 70% by volume of an unsupported catalyst and 30% by volume of a supported catalyst with a support. The hydroprocessing was performed at a pressure of 160 kg/cm² and a temperature of 380°C. The hydroprocessed fraction was then subjected to isodewaxing (IDW) and hydrofinishing (HDF) to obtain a recycled lubricating base oil. For the thus obtained recycled lubricating base oil of Experimental Example, the properties before isodewaxing (semi-product) are as illustrated in Table 3 below, and the properties after isodewaxing and hydrofinishing (prototype product) are as illustrated in Table 4 below. Table 3

100D

KV 100°C, cSt 4,069

VI/PP (°C) 133/-6

Table 4

4cSt prototype product(CDW reaction preparation)

KV 100°C, cSt 4.15

VI 132

PP, (°C) -18

Comparative Experiment Example

Another recycled lubricating base oil was obtained under the same feed and process conditions as in Experimental Example, except that the proportion of the supported catalyst was 100% by volume and the unsupported catalyst was excluded in the hydroprocessing step. The properties of the thus obtained recycled lubricating base oil (prototype product) of Comparative Experimental Example are as illustrated in Table 5 below.

Table 5

	Properties of prototype product
Kinematic Viscosity @ 40°C, cSt	20.56
Kinematic Viscosity @ 100°C, cSt	4.266
Viscosity Index	113
Pour Point, °C	-18
S/N/Cl, ppm	1/1/2
Metal, ppm	Trace

The prototype products of Experimental Example and Comparative Experimental Example were similar in other properties, but the viscosity index of the prototype product of Experimental Example exceeded 130, while that of the prototype product of Comparative Experimental Example was only 113, showing a large difference. This is believed to be due to the difference in the proportion of the unsupported catalyst in the catalyst used in the hydroprocessing step.

Claims

A method for producing a recycled lubricating base oil from waste lubricating oil, the method comprising:
a) a first pretreating step of pretreating a waste lubricating oil;

b) a distillation step of performing distillation to recover a fraction having a specific boiling point from a first pretreated waste lubricating oil recovered in step a);

c) a second pretreating step of pretreating the fraction recovered in step b); and

d) a hydroprocessing step of hydroprocessing the second pretreated fraction recovered in step c) in the presence of a catalyst.
The method of claim 1, wherein the waste lubricating oil prior to step a) has a viscosity index of equal to or less than 120, a sulfur content of equal to or greater than 10,000 ppm, and a nitrogen content of equal to or greater than 300 ppm.
The method of any preceding claim, wherein step a) comprises coagulant addition, centrifugal separation, or a combination thereof.
The method of any preceding claim, wherein step b) comprises atmospheric distillation, wherein the atmospheric distillation is preferably carried out at a temperature of 50°C to 350°C.
The method of any preceding claim, wherein step b) comprises vacuum distillation, which is preferably carried out at a pressure of equal to or less than 10 torr, or a temperature of 150°C to 600°C, or both.
The method of claims 4 and 5, wherein step b) comprises a combination and preferably a sequence of atmospheric distillation and vacuum distillation, wherein preferably a fraction having a boiling point of equal to or greater than 150°C is collected from the atmospheric distillation and this fraction is then subjected to the vacuum distillation, which yields the fraction recovered in step b).
The method of any preceding claim, wherein the fraction recovered in step b) has a boiling point of 300°C to 500°C.
The method of any preceding claim, wherein step c) comprises solvent extraction.
The method of claim 8, wherein the solvent used for the solvent extraction includes one or more ofN-methyl-2-pyrrolidone (NMP), sulfolane, dimethylsulfoxide (DMSO), furfural, phenol, and acetone.
The method of claim 8 or 9, wherein the solvent extraction is performed at a temperature of 60°C to 80°C, a solvent-oil ratio of 1.5:1 to 2.5:1 by volume, or both.
The method of any preceding claim, wherein, in step d), a proportion of an unsupported catalyst in the catalyst is 20% to 70% by volume, preferably 30% to 60% by volume, more preferably 40% to 50% by volume.
The method of any preceding claim, wherein the catalyst used in step d) comprises a metal, and the metal comprises Ni, W, Mo, Co, or a combination thereof, preferably in the form of an oxide.
The method of any preceding claim, wherein the method further includes: e) a step of dewaxing and/or hydrofinishing the hydroprocessed fraction recovered in step d).
A recycled lubricating base oil having a sulfur content of equal to or less than 5 ppm, a saturation of equal to or greater than 90%, and a viscosity index (VI) of equal to or greater than 130.
The recycled lubricating base oil of claim 14, wherein the recycled lubricating base oil has a kinematic viscosity of 4 to 5 cSt at 100°C and a pour point of equal to or less than -15°C.