Method and system for producing base oil with upstream hydroprocessing and downstream solvent extraction

Abstract

A method of processing used oils to produce base oils comprises physically separating contaminants from used oils to produce physically-purified stream; and chemically treating the physically-purified stream in a hydroprocessing reactor to produce chemically-treated stream comprising chemically-treated used oils. A first portion of the chemically-treated stream is recycled through the reactor to increase a total volumetric flow rate through the reactor and reduce hot spots and runaway reactions in the reactor. A second portion of the chemically-treated stream is contacted with an extraction solvent to produce an extract stream and a raffinate stream, the extraction solvent selected to dissolve selected soluble compounds in the chemically- treated stream. The hydroprocessing in the reactor decreases the concentration of polar molecules and increases the concentration of saturates in the chemically-treated stream, and increases the viscosity index of the chemically-treated stream. A system for performing the method is also provided.

Description

METHOD AND SYSTEM FOR PRODUCING BASE OIL WITH UPSTREAM HYDROPROCESSING AND DOWNSTREAM SOLVENT EXTRACTION

[0001] FIELD The present disclosure relates generally to processes and systems for rerefining or upgrading used oils to produce high quality base oils.BACKGROUND

[0002] Base oil is also referred to as base stock, base lube stock, lube stock, lube oil, lubrication oil, or the like. Base oil can be used to produce products with lubrication properties, such as lubricating oil or metal working fluids or hydraulic fluids.

[0003] Base oils can be produced by refining crude oils, such as paraffinic crude oil or naphthenic crude oil, using different processing techniques and facilities. For example, crude oils may be subjected to heating and distillation processes to separate light and heavy hydrocarbons, and the heavy hydrocarbons are further subjected to hydroprocessing to remove sulfur and aromatics, thus producing base oils with higher proportions of saturates, lower sulfur compound contents, and higher viscosity. Base oils can also be produced by re-refining used motor oil (UMO). In a typical re-refining process, contaminants are removed from the UMO, and distillations are performed to remove undesirable light materials and undesirable heavy materials. The resulting oil product may be further processed to upgrade the product to achieve certain desired parameters, such as a desired content of saturates, purity level, or viscosity index (VI).

[0004] Base oils are classified into different groups according to standards set out by the American Petroleum Institute (API). According to the current API classification (API 1509), Groups I, II and III are classified based on their physical and compositional properties. Specifically, Groups I, II and III are principally characterized and distinguished by their saturate levels, sulfur concentration, and viscosity index (VI).

[0005] The viscosity index is a measure of the change of viscosity with temperature, typically measured at 100 °F (40 °C) and 212°F (100 °C). ASTM D2270 (Standard Practice for Calculating Viscosity Index from Kinematic Viscosity) is normally used as the basis for calculating VI. Kinematic viscosity can be measured according to ASTM D445.

[0006] Base oils with higher saturate levels, lower sulfur levels, and a higher viscosity index are considered higher quality base oils. For example, according to the current API classification (API 1509), different Groups of base oils meet the requirements listed in Table I.TABLE I Classification of Base Oils

[0007] The parentheses in Table I indicate that Group I base oils may have either less than 90% saturates, or more than 0.03% sulfur, or both; but the VI is at least 80 and not more than 120. Group II base oils have at least 90% saturates and at most 0.03% sulfur, with 80 < VI < 120. Group III base oils have at least 90% saturates and at most 0.03% sulfur, and VI of at least 120. All percentages herein are mass percent (denoted as wt %) based on the total mass of the base oil including any impurities and additives, unless otherwise specified. Some Group II base oils have one or more properties better than the minimum standard requirements for Group II base oils but do not meet all of the requirements for Group III oils, and such Group II base oils may be referred to as Group II+ base oils. For example, a Group II+ base oil may have a VI above 110.

[0008] Group II and Group III base oils may be considered as high-quality base oils(HQBO).

[0009] Used oils, such as used motor oils (UMO), can be re-refined to produce higher quality base oils. For example, systems and methods for producing Group II or Group III base oils and other products from used oils have been proposed, where the used oil is subjected to, in sequence, distillation, solvent exchange, and hydrotreatment treatments. A drawback of such a conventional process is that it is difficult to improve the overall yield and performance of the solvent exchange and hydrotreatment processes.

[0010] Therefore, it is desirable to improve systems and methods for producing high quality base oils such as to improve overall yield and efficiency.SUMMARY

[0011] Processes and systems for re-refining used oils are provided herein with a view to increase the quality and yield of primary Group III base oil products.

[0012] In an aspect, there is provided a method of processing used oils to produce base oils, comprising physically separating contaminants from a feed of used oils to produce a physically-purified stream comprising purified used oils and a stream comprising the contaminants, the physically separating comprising distillation; chemically treating the physically-purified stream to produce a chemically-treated stream comprising chemically- treated used oils, the chemically treating comprising hydroprocessing in a reactor in the presence of a catalyst selected for at least hydrodesulfurization, hydrodenitrogenation and hydrogenation, wherein a first portion of the chemically-treated stream is recycled through the reactor to increase a total volumetric flow rate through the reactor and reduce hot spots and runaway reactions in the reactor; and contacting a second portion of the chemically-treated stream with an extraction solvent to produce an extract stream and a raffinate stream, the extraction solvent selected to dissolve selected soluble compounds in the chemically-treated stream, wherein the extract stream comprises the extraction solvent and the selected soluble compounds dissolved in the extraction solvent. Thehydroprocessing decreases the concentration of polar molecules and increases the concentration of saturates in the chemically-treated stream, and increases the viscosity index of the chemically-treated stream.

[0013] In various embodiments of the method described in the preceding paragraph, one or more of the following features may be included. The raffinate stream may comprise a base oil having a viscosity index of greater than 120, a concentration of sulfur of less than 0.03 wt%, and a concentration of saturates higher than 90 wt%. The chemically treating may comprise adding hydrogen to the physically-purified stream to form a first liquid mixture of the physically-purified stream and hydrogen dissolved therein; passing the first liquid mixture through a guard bed comprising a catalyst to remove metal elements and produce a second liquid mixture comprising reduced metal elements; and feeding the second liquid mixture to the reactor to produce the chemically-treated stream. The first portion of the chemically-treated stream may be added to the second liquid mixture before feeding the second liquid mixture to the reactor. The temperature of the first liquid mixture may be from 325 °C to 400 °C. The temperature of the second liquid mixture may be from 330 °C to 405 °C. The extraction solvent may be N-Methyl 2-Pyrrolidinone. The second portion of the chemically-treated stream and the extraction solvent may be contacted in a continuous flow solvent extraction column. The solvent extraction column may comprise a variable speed agitator. The method may comprise further treating the raffinate stream to extract the base oil. The method may comprise treating the extract stream to recover the extraction solvent and produce another base oil.

[0014] In another aspect, there is provided a system for processing used oils to produce base oils, comprising a physical separation subsystem for physically separating impurities and contaminants from a feed of used oils to produce a physically-purified stream comprising purified used oils and a stream comprising the impurities and contaminants, the physical separation subsystem comprising a plurality of distillation vessels; a chemical treatment subsystem for chemically treating the physically-purified stream to produce a chemically-treated stream comprising chemically-treated used oils,the chemical treatment subsystem comprising a hydroprocessing reactor comprising an inlet connected to the physical separation subsystem, an outlet, and a catalyst selected for at least hydrodesulfurization, hydrodenitrogenation, and hydrogenation, to reduce concentrations of sulfur, nitrogen, and polar molecules, and increase concentrations of saturates in the chemically-treated stream, and to increase a viscosity index of the chemically-treated used oils; a conduit connecting the outlet of the hydroprocessing reactor to the inlet of the hydroprocessing reactor, for recycling a first portion of the chemically-treated stream through the hydroprocessing reactor to increase a total volumetric flow rate through the hydroprocessing reactor and eliminate hot spots and runaway reactions in the hydroprocessing reactor; and a solvent extraction column connected to the outlet of the hydroprocessing reactor for receiving and contacting a second portion of the chemically-treated stream with an extraction solvent to produce an extract stream and a raffinate stream, the extraction solvent selected to dissolve selected soluble compounds in the chemically-treated stream, wherein the extract stream comprises the extraction solvent and the selected soluble compounds dissolved in the extraction solvent, and the raffinate stream comprises a base oil having a viscosity index of greater than 120, a concentration of sulfur of less than 0.03 wt%, and a concentration of saturates higher than 90 wt%.

[0015] In various embodiments of the system described in the preceding paragraph, one or more of the following features may be included. The hydroprocessing reactor may be configured and the catalyst may be selected to convert linear paraffinic compounds in the physically-purified stream to branched chain molecules and cause ring opening reactions. The chemical treatment subsystem may comprise a hydrogen source for adding hydrogen to the physically-purified stream to form a first liquid mixture, a guard bed comprising a catalyst disposed downstream of the distillation vessels and upstream of the hydroprocessing reactor, for removing metal elements from the first liquid mixture and producing a second liquid mixture comprising reduced metal elements; and a conduit connecting the guard bed to the inlet of the hydroprocessing reactor to feed the secondliquid mixture to the hydroprocessing reactor. The catalyst in the hydroprocessing reactor may comprise a nickel-molybdenum, cobalt-molybdenum, or nickel-tungsten catalyst, or another metal catalyst comprising one or more metal elements, or any combination thereof. The hdyroconversion reactor may be configured to operate at a temperature of 330 °C to 405 °C. The guard bed may comprise a nickel or vanadium catalyst and may be configured to operate at a temperature of 325 °C to 400 °C. The solvent extraction column may comprise a variable speed agitator. The system may comprise a recovery subsystem for recovering the extraction solvent from the extract stream and for recovering a further base oil from the extract stream.

[0016] In some embodiments, used oils may be subjected to a series of distillation and vacuum evaporation steps where high vacuum distillation is used to recover VGO (Vacuum Gas Oil) fractions contained in the used oil. The distillation temperatures may range between approximately 135 °C (280 °F) and 325 °C (620 °F). The VGO fraction may be routed to a hydroprocessing unit, where hydroprocessing is carried out in the continuous liquid phase. The hydroprocessing reactor may be protected by a guard bed reactor operating at temperatures ranging from 325 C° to 400 °C (617 to 750 °F). The guard bed catalyst may include nickel or vanadium or any of the Group VIII elements. The hydroprocessing reactor, operating at temperatures ranging from 330 C° to 405 °C° (625 to 760 °F), may have a catalyst of nickel-molybdenum, cobalt-molybdenum, nickel-tungsten, or similar single and / or mixed metal catalysts. Hydrogen may be continuously added to the liquid mixture at a constant pressure and the catalyst may promote reaction of hydrogen with other molecules, such as with unsaturated hydrocarbons to form saturates, with sulfur to form H2S, and with nitrogen to form NH3.The hydroprocessing reactor may include three stacked or superimposed sections, may be operated at typical pressures of 35 atm to 200 atm (3500 to 20,200kPa / 515 to 2900 psi) and may include reactions that saturate double bonds, desulfurize / denitrogenize, convert linear paraffinic compounds into branched chain molecules and open ring compounds. The hydroprocessing reactor catalyst may be selected to promote certain reactions overothers, so the reactions in the hydroprocessing reactor are selective in favor of reactions involving molecules with lower lubrication value or properties, such as unsaturated hydrocarbons or non-saturates. A portion of the output stream from the reactor may be recycled back to the reactor. The recycled stream provides a portion of the needed hydrogen to the reactor, and may also function as a heat sink, thus further reducing temperature fluctuations in the reactor, resulting in the treatment process in the reactor being more isothermal.

[0017] In some embodiments, the hydroprocessing unit may allow and promote hydrogen reactions with many of the components in the physically-purified stream, including the polar molecules, resulting in an increased concentration of saturates and a decreased concentration of polar molecules, thereby allowing the solvent in the downstream solvent extraction to be more efficient with extracting less polar materials as compared to processes and systems previously disclosed in the literature. A method as disclosed herein also increases the viscosity Index of the base oil products, which may contain Lube Oils.

[0018] In some embodiments, a portion of the chemically-treated stream may be processed in an agitated solvent extraction column by contacting it with a solvent in a counter-current method with a variable speed agitator. The volume ratio of the extraction solvent to the feed may be from about 1 to about 4. The extract temperature may range from 35 °C to 70 °C (95 to 158°F). The outputs from the solvent extraction column may include a lighter phase, the raffinate, and a heavier phase, the extract. Due to the increased concentration of saturates and lower concentration of polar molecules in the chemically-purified stream, the raffinate phase, which has some residual solvent, may contain a higher viscosity index Group III base oil with an increased yield. The extract phase, after further distillation, may contain a Group II / II+ base oil product.

[0019] In some embodiments, a used oil feedstock may be physically purified to create a vacuum gas oil product operating at distillation temperatures between 135 and 325 °C. The vacuum gas oil may be routed to a hydroprocessing system, operating at temperatures ranging from 325 °C to 405 °C, where hydrogen reactions create more saturates and less polar compounds to improve yield and increase the viscosity index of the oil. This increase in saturates reduces the content of lower quality base oil and therefore the operating burden on the solvent, which is contacted with the oil at a solvent to feed ratio ranging from 1 to 4, and combined with the VI increase, results in an improved yield with higher quality Group III base oil with a VI greater than 120, a sulfur concentration less than 0.03 wt%, and a concentration of saturates higher than 90 wt%. The extraction solvent and feedstock may be agitated by a variable speed agitator at a selected agitation speed. The extract may be further processed in a distillation system with Group II / II+ base oil being produced with a VI of greater than 110, a sulfur concentration less than 0.03 wt%, and a saturates concentration higher than 90 wt%. The raffinate may be further treated to remove residual solvent to produce a Group III base oil.

[0020] Other aspects, features, and embodiments of the present disclosure will become apparent to those of ordinary skill in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures.BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In the figures, which illustrate, by way of example only, embodiments of the present disclosure:

[0022] FIG. 1 is a schematic diagram illustrating a system and process for producing and upgrading base oils, according to an example embodiment of the present disclosure; and

[0023] FIG. 2 is a schematic diagram of a particular example of the system of FIG. 1 , including a physical contaminant separation unit (CSU), a molecular treatment unit (MTU); and a molecular separation unit (MSU).DETAILED DESCRIPTION

[0024] In brief overview, an aspect of the present disclosure relates to processes and systems for producing base oils from used oils and upgrading the base oils with improved yield of high quality base oils (HQBO), including Group II and Group III base oils. The used oils may be used motor oils (UMO). The HQBO can be used as lubrication oils, also referred to as lube oils.

[0025] In an embodiment disclosed herein, used oils are initially physically purified, such as by a conventional purification or contaminant removal process, including filtering, solid removal, and multiple fractional distillations. The physically purified used oil is then subjected to chemical treatment including hydroprocessing to produce a chemically treated purified oil, with a reduced sulfur content and an increased viscosity index. The chemically treated purified oil is then subjected to solvent extraction with an extraction solvent to separate the polar and lower quality components from high quality base oil components.

[0026] It has been recognized that upstream hydroprocessing can conveniently increase the saturates and lower the polar molecules content in the chemically treated purified oil, thereby reducing the operating burden on the extraction solvent. Further, the chemically treated purified oil has reduced amounts of impurities, as some of the impurities have been hydroprocessed and removed. Thus, the performance of the downstream solvent extraction process can be improved, with e.g., improved yield and efficiency. It is also expected that the characteristics of hydrogenated molecules can favorably affect the selectivity of the solvent extraction to improve the viscosity index (VI) of the base oil products produced.

[0027] Further, it has been recognized that performing hydroprocessing upstream of the solvent extraction would not significantly increase the usage of hydrogen in the chemical treatment process, as compared to performing hydroprocessing downstream of the solvent extraction. In particular, the sulfur and nitrogen species in the used oils generally partitioned with the extraction solvent so the quantities of nitrogen and sulfur species in the streams to be treated in the hydroprocessing reactor would be relatively consistent in either arrangement. As a result, the hydrogen consumption for hydrodesulfurization and hydrodenitrogenation would be similar regardless of whether the hydroprocessing is performed upstream or downstream of the solvent exchange process.

[0028] In addition, it has been recognized that performing hydroprocessing upstream of solvent extraction would not necessarily significantly reduce the catalyst lifetime or reduce the performance of the hydroprocessing reactor.

[0029] Further, it has been recognized that recycling a portion of the chemically treated purified oil back to the hydroprocessing reactor would also further increase the fluid volume and flow rate through the reactor and improve temperature control in the reactor.

[0030] In view of the above factors, it can be expected that performing the hydroprocessing upstream of the solvent exchange can improve overall yield and performance of the process and improve the VI of the HQBO stream.

[0031] In a particular embodiment, a method of processing used oils to produce base oils includes physically separating contaminants from a feed of used oils to produce a physically-purified stream comprising purified used oils and a stream comprising the contaminants. The physically separating process may include distillation and other physical separation processes. The physically purified stream is chemically treated to produce a chemically treated stream comprising chemically treated used oils. The chemical treatment includes hydroprocessing in a reactor in the presence of a catalyst. A portion of the chemically treated stream is recycled through the reactor to increase the total volumetric flow rate through the reactor and avoid localized zones of hightemperatures (hot spots), runaway reactions, and fouling in the reactor. Another portion of the chemically treated stream is contacted with an extraction solvent to produce an extract stream and a raffinate stream. The extraction solvent is selected to dissolve selected soluble compounds in the chemically treated stream for separating and removing the dissolved compounds. The hydroprocessing conveniently reduces the sulfur content in the chemically treated stream, increases the saturates content, reduces the polar molecules content, increases the viscosity index of the chemically treated stream, reduces the operating burden on the extraction solvent, and increases the lifetime of the extraction solvent as the solvent has fewer contaminants to extract. The hydroprocessing may also conveniently remove other impurities such as nitrogen.

[0032] In previous base oil upgrading processes, such as those described in US 8,366,912 and US 9,677,013, hydrotreatment is performed downstream of the solventexchange process. It is expected that, in comparison with these previous processes, performing hydroprocessing upstream of solvent-exchange as described herein can improve the overall product yield, efficiency, and performance without increased usage of hydrogen and catalyst.

[0033] FIG. 1 illustrates an example base oil production system 5.

[0034] System 5 incudes a physical separation subsystem 10 for physically purifying a feed of used oils to remove contaminants and impurities. The physical separation subsystem 10 may include a processing subsystem referred to as contaminant separation unit (CSU), which will be further described below.

[0035] The term “used oil” as used herein includes any petroleum, or natural or synthetic oils, that have been used, and as a result of such use are possibly contaminated by contaminants or impurities, and thus have deteriorated physical or chemical properties. The used oils are typically of a lower quality than the original un-used oils. Used oils may include waste oils. Used oils may include used motor oils (UMO), or used industrial oils. For example, used oils may include used industrial lubricants. UMO may be obtained fromvarious sources, such as automobiles, passenger motor cars, engines, industrial plants, or the like. Used oils from different sources can have different properties and constituents.

[0036] It is noted that used oils are different from crude oils in their compositions and properties. Crude oils refer to oils extracted from subterranean reservoirs. For example, UMO typically contains contaminants that are not present in crude oils, which contaminants may include contaminants introduced during manufacture of the motor oil or during use of the motor oil, and external contaminants such as salt and water. Consequently, the processing and treatment techniques for refining crude oils and rerefining used oils have been quite different in conventional refineries or refining technologies.

[0037] Used oils may include used engine oils. Typically, high quality base oils are blended with about 15 to 25 wt% performance additives to produce engine oils. These additives are always present in the used engines oils or UMO. The additives may include viscosity modifiers (VM), detergents and dispersants, depressants, antiwear additives, antioxidants, corrosion inhibitors, metal passivators, antifoam additives, sulfur scavengers, or the like.

[0038] Contaminants can be formed or introduced in to the engine oils during use. For example, common external contaminants or contaminants formed by engine gear or material degradation include water, other automotive fluids such as fuel oil and fuel additives, transmission fluids, brake fluids, waste gasoline, non-automotive lubricants, or industrial oils such as hydraulic fluids, dirt, salt, sludge, soot, carbonaceous particles, lacquer, oxidation products, or the like. Contaminants formed from the additives or due to engine wear-and-tear may include metals, metallic oxides or particles, and polymers. The contaminants may include zinc, calcium, phosphorus, silicon, or the like. In particular, phosphorus and silicon are difficult to remove by distillation and may poison hydroprocessing catalysts. UMO may also contain coolants, such as ethylene and propylene glycol.

[0039] Used oils such as UMO may contain about 75 wt% to 85 wt% lube oil molecules, which can re-refined and recovered to form higher quality base oils. In some embodiments, the main contaminants to be removed from the UMO are water, sludge, corrosion precursors and catalyst poisons.

[0040] The used oils may be pre-treated or purified to provide purified used oils. In this disclosure, “purified oils” refer to any used oils or crude oils that have been subjected to one or more purification treatment(s) to remove impurities such as water, light fuel, or other chemical compounds including ethylene glycol, particulate materials, metals, either completely or partially. Water may be removed by a dehydration process. The purification process may also include distillation, such as vacuum distillation. In purified used oils, some impurities or contaminants may still exist. Different purification processes may be used to remove different impurities and contaminants. Depending on the particular application, not all impurities or contaminants need to be removed before refining or upgrading. In some cases, only certain selected types of impurities or contaminants are removed. In some cases, a certain percentage of impurities or contaminants may remain in the purified used oils.

[0041] Partially purified oils with various impurities / contaminants at various levels (percentages) may be used in different applications without further purification or rerefining or upgrading. For example, in some relevant industries, partially purified oils may include oils that are referred to as vacuum gas oil (VGO), light VGO (LVGO), heavy VGO (HVGO), marine fuel oil (MGO), or the like, or oils that have similar constituents or properties thereof.

[0042] The physically purified oils can also be distillates including partial distillates obtained by distilling used oils. The distillation process may include flash distillation of used oils. In some embodiments, atmospheric distillation or vacuum distillation may also be included. In the relevant industry, the term “distillates” may also refer to diesel fuel, fuel oil, heating oil, or the like. Typically distillates may also have an initial boiling point (IBP) ofabout 200 °C (390 °F) and a final boiling point (FBP) of 370 °C (700 °F). Typical partial distillates may have an IBP-FBP range that overlaps with the range of 200 to 370 °C (520 to 700 °F). For example, a partial distillate may have an IBP-FBP range of 150 - 250 °C (300 - 480 °F), or 250 - 425 °C (480 - 800 °F). VGO and MGO are examples of distillates.

[0043] As discussed earlier, in some embodiments, the physical separation subsystem 10 may include a contamination separation unit (CSU) to physically separate and remove various contaminants from the used oil and obtain a partially purified oil fraction. Because at least some potential contaminants can cause plugging, fouling, or corrosion in the downstream processing facilities, removing such contaminants can reduce or avoid plugging, fouling and corrosion, and improve the overall system performance and efficiency. The CSU may include one or more stages, steps, or subunits for removing or separating contaminants from used oils as described in, e.g., US 8,366,912 (as “Stage #1”), US 8,936,718 (as “Stage #1”), US 9,677,013 (as Steps #1 to #3), US 10,287,513 (as Stage #1), US 10,287,513 (as Stage #1), and US2022 / 0089968 (CSU), the contents of each of which are incorporated herein by reference.

[0044] For example, the CSU may include devices for multistep evaporation and distillations of the used oil, which may have been already partially purified to remove some contaminants such as solids. The CSU may also include a dehydration step, where the used oil is preheated to vaporize and remove water. The portions removed at this step may include water, light hydrocarbons, and contaminates, additives and degradation products.

[0045] The dehydrated oil may be then routed to a stripper operated under vacuum conditions, to remove light gas oil components, so as to produce a fluid that may have a flash point and a viscosity index suitable for producing Group II / II+ and Group III base oils by further treatments described herein.

[0046] The fluid stream may be next subjected to high vacuum distillation to recover the VGO fraction contained in the used oil. Upon entering the column, the stripped oil flashesunder the deep vacuum conditions. The liquid flows to the bottom and enters evaporators. The evaporation is performed at high temperature. Due to the high temperature and the thermally unstable nature of the contaminants, vaporization of these heavy hydrocarbons may be carried out by thin film evaporators (TFE) or wipe film evaporators, to prevent fouling, cracking and to guarantee a homogeneous temperature distribution.

[0047] The vapors from the evaporators flow up to the fractionation columns and are distilled under vacuum conditions. The liquid condensed on the top packing is the main product, VGO. The VGO is routed to the chemical treatment subsystem for further processing as will be described below.

[0048] In different embodiments, the CSU may include a packed tower, commonly referred to as a packed column. For example, the packed column may be in the form of a generally cylindrical vessel filled with packing materials. The feedstock is typically circulated from the top to the bottom, and a purifying agent such as soda ash or potassium hydroxide may be injected in the liquid phase into the column at the top of column. The soda ash may be injected using spray nozzles provided at the top of the column.

[0049] In some embodiments, the CSU may include a vacuum separation column, instead of a thin film evaporator commonly used for separating contaminants in crude oil refineries. The CSU may also include a distillation facility for removing water and other impurities or contaminants based on the boiling points or vapor pressure of the materials. The feedstock may include used oils, such as UMO or used industrial oils, or a combination thereof. While UMO is sometimes referred to herein when describing and illustrating the operation of the process and system as depicted in the drawings, other used oils may also be used as or in the feedstock. The feedstock may contain various contaminants, which may include water, light hydrocarbons, solvents, solids, polymers, high molecular weight hydrocarbons, lubricating oil additives, chemicals, salts, and the like.

[0050] Various physical contaminants may be removed from the base oil fraction andthe gas fraction. The removed physical contaminants may be separated into more than one output streams through more than one outlet lines. The removed physical contaminants may include materials such as water, glycols, asphalts, or the like. The removed contaminants may also include impurities in the gas phase. Some sulfur in the feedstock may also be removed in the CSU. Sulfur may be reacted with a chemical agent to form precipitates. The precipitates can then be removed with other separated contaminants such as asphalts. Several processes or combination of processes known to those skilled in the art can be used to effect physical separation in the CSU. Typically, physical separation will be effected based upon some differences in physical or chemical properties of the materials to be separated. Various convention systems and techniques may be used to effect separation in the CSU. The purified oil fraction output from the CSU contains a reduced proportion of impurities or contaminants, as compared to the feedstock. The vacuum gas oil extracted from the CSU may include saturated and unsaturated hydrocarbons suitable for use as, or for further processing to produce, base oils. Suitable hydrocarbon molecules for base oils typically have 18 to 40 carbon atoms and having a boiling temperature of about 260 °C (500 °F ) to about 650 °C (1200 °F ) at 1 atm (100 kPa or 15 psi).

[0051] Additional features and details of an example CSU will be described below with reference to FIG. 2.

[0052] The physically purified stream from the subsystem 10 is passed to a subsystem 20 for chemical treatment, including hydroprocessing. The hydroprocessing may include hydrodesulfurization, hydrodenitrogenation, hydrogenation, and catalytic hydrotreating. In selected embodiments, hydroprocessing includes hydrotreatment for reducing the heteroatom content in the chemically treated stream, which may involve one or more of saturation reactions, and ring-opening reactions or other bond-breaking reactions that convert unsaturated hydrocarbons or hydrocarbons with double bonds, such as olefinic hydrocarbons, aromatic hydrocarbons, and naphthenic hydrocarbons, to paraffinic hydrocarbons. As can be understood by those skilled in the art, paraffinic hydrocarbonstypically exhibit higher viscosities, as compared to unsaturated, aromatic, or naphthenic hydrocarbons.

[0053] Possible and representative hydroprocessing reactions in the hydroprocessing reactor may include the following, where R is a hydrocarbon group:(i) RSR’ + H2H2S + R + R’(ii) RN + 2H2^ RH + NH3(iii) ROH + H2RH + H2O(iv) C5H10 + H2— > CSHI2

[0054] Some hydrogenated compounds, such as H2S, NH3, and water, are separated and removed from the chemically treated used oils. Hydroprocessing can also reduce levels of aromatics, naphthenics, and olefins in the chemically treated used oils and increase the concentrations or levels of saturates in the chemically treated used oil, with the effect of increased viscosity index. The hydroprocessing may also convert some polar compounds to non-polar compounds or reduce the polarity of the chemical treated stream. The hydroprocessing may reduce the levels of sulfur, nitrogen, aromatics, naphthenics, olefins, polar compounds, unsaturates, heteroatoms, and the like in the chemically treated stream. Other possible contaminants that may be present in the physically purified used oil stream and may be removed by subsystem 20 may include metals, phosphorus, or the like.

[0055] The hydroprocessing may be performed in a continuous flow liquid phase reactor. The chemically treated used oils are thus suitable for producing HQBO including Group III base oils by further treatment such as solvent exchange.

[0056] The chemically treated used oil is subject to solvent extraction treatment with the extraction solvent in subsystem 30.

[0057] Subsystem 30 may include a solvent extraction column designed to perform continuous liquid-liquid solvent extraction, and the fluids flowing through the solvent extraction column may be agitated with a variable speed agitator. The extraction solvent may be N-Methyl 2-Pyrrolidinone (NMP). The chemically treated used oil stream and the extraction solvent stream may form counter-currents in the extraction column. The outputs from the solvent extraction column includes an extract stream and a raffinate stream. The raffinate stream contains a HQBO including Group III base oil. Some lower quality components in the chemically treated used oil stream are dissolved in, and removed with the extraction solvent, which flows in the opposite direction as the raffinate stream.

[0058] The raffinate stream separated from the extract stream may contain base oils of a higher quality because the raffinate stream may have a higher level of saturates, a lower level of sulfur, and a relatively higher VI. The raffinate stream may also have a reduced level of naphthenics and aromatics.

[0059] Subsystem 30 may include a stripper column operating under vacuum for removing any residual solvent in the raffinate stream from the end oil product which contains Group III base oils.

[0060] The extract stream initially contains most of the extraction solvent, which can be subsequently separated and removed, as will be further discussed below. The extract contains a base oil that has a lower level of saturates and a lower viscosity index (VI) as compared to the base oil in the raffinate stream.

[0061] The oil product produced in subsystem 30 may include base oils containing at least 90 wt% saturates and less than 0.03 wt% sulfur, and having a VI of at least 120. In some embodiments, the oil product may contain at least 95 wt% saturates.

[0062] The extract stream from Subsystem 30 is further treated in Subsystem 40 to recover the extraction solvent and produce another base oil product, which also contains HQBO but may have a lower quality than Group III base oil, such as Group II or Group II+base oils.

[0063] Subsystem 40 is a recovery subsystem configured to recover the extraction solvent and produce further base oil products, and may include distillation vessels for separating the solvent from the base oil components to recover the solvent and a further base oil product, as can be understood by those skilled in the art.

[0064] Subsystem 40 may use steam to strip the extraction solvent from the oil components separated from the extract stream.

[0065] Subsystem 40 may include an extract distillation column operating under vacuum. Most of the solvent in the extract stream may be removed from the base oil components as an overhead stream from the extract distillation column. Subsystem 40 may further include an extract stripper column operating under vacuum, which uses steam to strip solvent from the base oil components output from the extract distillation column. The remaining solvent is steam stripped out of the stream, producing a base oil product containing Group 11 / 11+ base oils. The oil product produced by subsystem 40 may include base oils containing at least 90 wt% saturates and less than 0.03 wt% sulfur, and having a VI of at least 80. In some embodiments, the oil product may contain at least 95 wt% saturates.

[0066] FIG. 2 illustrates further details of the system 5 according to a specific embodiment.

[0067] The system illustrated in FIG. 2 includes a contaminant separation unit (CSU) 10’ for physically purifying a feedstock of used oil, a molecular treatment unit (MTU) 20’ for chemically treating the physically purified used oil, a molecular separation unit (MSU) 30’ for separating certain components from the base oil components in the chemically treated stream by solvent extraction, and an extract treatment unit 40’ for treating the extract.

[0068] The CSU 10’ includes a multistep distillation system for separating base oilfraction from other components in the feedstock introduced through input line 42. The feedstock may be stored in a feedstock storage (not shown) or provided by any suitable manner, such as by transportation or pipelines.

[0069] More specifically, CSU 10’ includes an input line 42, heat exchangers 44, 84, 104, 128, transport lines 46, 56, 78, 82, 83, 86, 98, 102, 106, 108, 120, 124 and 126, a first flash distillation vessel 52, a second in-situ flash distillation vessel 70, a third vacuum distillation vessel 90, a fourth vacuum distillation vessel 112 and pumps 80, 100, 122.

[0070] The flash distillation vessel 52 includes a distillate output line 54 for outputting the distillate stream produced therein. Line 56 is a bottom outlet line for transporting the bottom stream formed in flash distillation vessel 52 to the flash distillation vessel 70.

[0071] The flash distillation vessel 70 includes a distillate output line 76 for outputting the distillate stream produced therein. Line 78 is a bottom outlet line for transporting the bottom stream formed in flash distillation vessel 70 through pump 80, line 82 and heater 84, to the flash distillation vessel 90 through line 86, or to the recycling line 83 that feeds back into the flash distillation vessel 70. Pump 80 drives the fluid flow in transport lines 78, 82, 83, and 86. Heater 84 heats the fluid transported through line 82.

[0072] The vacuum distillation vessel 90 includes a distillate output line 96 for outputting the distillate stream produced therein. Line 98 is a bottom outlet line for transporting the bottom stream formed in vacuum distillation vessel 90 through pump 100, line 102 and heater 104, to the vacuum distillation vessel 112 through line 106, or to the recycling line 108 that feeds back into the vacuum distillation vessel 90. Pump 100 drives the fluid flow in transport lines 98, 102, 106, and 108. Heater 104 heats the fluid transported through line 102.

[0073] The vacuum distillation vessel 112 includes a distillate line 118 outputting the distillate stream produced therein. Line 120 is a bottom outlet line for transporting the bottom stream formed in vacuum distillation vessel 112 through pump 122, line 124 toprovide an oil product or further processing, or to recycle the bottom stream (or a portion thereof) back to the vacuum distillation vessel 112 through line 126, heater 128, and line 106. Pump 122 drives the fluid flow in transport lines 120, 124 and 126. Heater 128 heats the fluid transported through line 126.

[0074] During operation, the feedstock is introduced through line 42 and heated by heater 44 and before being introduced through line 46 into the first flash distillation vessel 52, and subjected to a distillation process in vessel 52. The distillation temperature in vessel 52 is controlled and adjusted to allow boiling of water and other light materials including fuel dilution and byproducts of combustion. A typical distillation temperature, depending on the contents of the feedstock and the operating pressure selected, may be in the range of from about 88 °C (190 °F) to about 204 °C (400 °F). The overhead stream is produced and collected at the top of the flash distillation vessel 52, The stream mainly consist of water, with some light hydrocarbons, which has a boiling point of up to about 275 °C (525 °F) at 1 atm. The bottom stream formed and collected at the bottom may include dehydrated oil fraction in the feedstock, and is withdrawn through the bottom outlet and line 56, and transported to the in-situ flash distillation vessel 70.

[0075] The first distillation process separates and removes light hydrocarbons and remaining water from the bottom stream of vessel 52.

[0076] The bottom stream of vessel 52 is subjected to further distillation in vessel 70. The distillation temperature in vessel 70 may be in the range of from about 138 °C (280 °F) to about 193 °C (380 °F). A distillate stream produced and collected at the top 72 of vessel 70 is output through outlet line 76. A bottom stream formed at the bottom of vessel 70 is discharged through outlet line 78 for recovering a portion of a liquid layer maintained in the lower portion of vessel 70.

[0077] The distillate stream recovered from line 76 has a boiling point of generally from about 175 °C (350 °F) to about 315 °C (600 °F). The distillate stream of vessel 70 can thus be used as fuel oil.

[0078] The bottom stream formed at vessel 70 contains a heavier oil. A fraction of the bottom stream of vessel 70 may be recycled back through line 78, pump 80, feed inlet line 82, heater 84, and line 83. Another fraction of the heated bottom stream in line 82 may be transported through line 86 to the third vacuum distillation vessel 90.

[0079] The heated bottom stream of vessel 70 is further distilled in vessel 90. The distillation temperature in vessel 90 may be in the range of about 138 °C (280 °F) to about 325 °C (620 °F). The distillate stream formed and collected at the top of vessel 90 also contains oils that can be used as fuel oil. The distillate stream has a boiling point of from about 200 °C (390 °F) to about 560 °C (1045 °F).

[0080] In this vacuum distillation process, non-volatile fractions including fuel fraction, gas oil, and heavy residual oil are separated.

[0081] The bottom stream formed and collected at the bottom of vessel 90 contains heavy oil. A portion of the bottom stream is recycled back to the vessel 90 after it is heated by heater 104, through lines 98, 102, 108 and pump 100. A portion of the heated bottom stream is passed through line 106 as a feed to the fourth vacuum distillation vessel 112. A liquid volume is maintained at the lower portion of vessel 90.

[0082] The returned heated bottom streams for vessels 70 and 90 are used to maintain the temperatures in the liquid layers at the bottom of the vessels 70 and 90 respectively.

[0083] The feeds into vessels 70 and 90 are heated to sufficiently elevated temperatures necessary to effect the desired separation of the distillates by direct contact with the liquid layer in the bottom of the vessels 70, 90.

[0084] The fraction of bottom stream fed into vessel 112 from vessel 90 is subjected to further distillation in vessel 112, at a higher temperature, up to about 295 °C (560 °F). Vessel 112 is configured and operated to produce a distillate stream at the top 114, which has a boiling temperature from about 285 °C (545 °F) to about 650 °C (1200 °F). Thedistillate stream is output through distillate outlet line 118.

[0085] A liquid level is also maintained at the bottom 116 in vessel 112. A portion of the bottom stream formed at the bottom is heated and recycled back to vessel 112 through line 120, pump 122, heat exchanger 128, and line 106. The returned heated bottom stream helps to maintain the desired feed temperature to vessel 112. The other portion is discharged through line 124 and may be used as a product or subjected to further processing. For example, the output from line 124 may be transported to a storage container (not shown) for storage.

[0086] Depending on the original feedstock, the bottom stream recovered through line 124 typically includes asphalt, polymers, high boiling point hydrocarbons, salts, solids, other high boiling point materials, which have a boiling point greater than about 650 °C (1200 °F).

[0087] In some embodiments, vessel 112 may be a vacuum distillation vessel, for example to prevent degradation of any base oil fractions in the feed to the vessel 112. Steam or gas stripping may also be used in vessel 112 to enhance distillation.

[0088] The distillate stream recovered from vessel 112 at line 118 contains physically purified used oil. Distillate from line 118 is condensed in 129 to become a liquid in line 130. The physically purified used oil may be partially purified as discussed earlier. The physically purified used oil is transported or supplied as the input stream to the MTU 20’ for hydroprocessing treatment.

[0089] The MTU 20’ may be a continuous flow liquid phase hydrotreatment unit containing a hydroprocessing catalyst.

[0090] Hydroprocessing may be carried out in the gas phase or liquid phase. However, a continuous liquid phase hydroprocessing process may be selected in combination with a continuous solvent treatment process as described herein to provide better temperaturecontrol, maintain continuous operation for an extended period, with easily adjustable or modifiable operation parameters, without the need to suspend the operation or process flow in either the CSU 10’ or MSLT 30’. Further, the lifetime of the hydroprocessing catalyst used in the hydroprocessing process may be prolonged. In particular, the input and output flow rates in various stages may be varied and adjusted, the hydroprocessing and solvent treatment can operate effectively and efficiently at various throughput or feedstock flow rates.

[0091] More specifically, the MTU 20’ includes a heat exchanger 201 , guard bed 202, a heat exchanger 203, and a hydroprocessing reactor 204. The heat exchanger 201 is located on the transport line 130 for heating the purified used oil stream output from distillation vessel 112 of CSU 10’. The MTU 20’ further includes a transport line 214 connecting the transport line 118 to the guard bed 202, an inlet 213 connected to the transport line 214, a transport line 215 connecting the guard bed 202 to the heat exchanger 203, a transport line 216 connecting the heat exchanger 203 to a first input port 221 of the hydroprocessing reactor 204, a transport line 212 for supplying hydrogen (H2) from a hydrogen source (not shown), a transport line 217 connecting transport line 212 to inlet 218 on transport line 216 and to input ports 219 and 220 of the hydroprocessing reactor 204, a transport line 222 connected to an output port of the hydroprocessing reactor 204, and a connection line 223 connecting transport line 222 to transport line 217 for recycling a portion of the chemically treated stream form line 222 back to the hydroprocessing reactor 204 through inlets 218, 219, 220.

[0092] Inlet 213 is used to add hydrogen to the purified used oil stream before it reaches the guard bed 202. Transport lines 212 and 217 are used to supply liquid hydrogen into the hydroprocessing reactor 204, through inlet 218 / input port 221 , and input ports 219, 220.

[0093] The guard bed 202 may have a top, a bottom, and a contact zone. In some embodiments, the contact zone may contain a spent catalyst or the like, which areselected to remove contaminants, such as silicon and phosphorus, from liquids passing through the guard bed 202, where the contaminants may have a negative effect on the hydroprocessing catalyst in the hydroprocessing reactor 204. Thus, the guard bed 202 can “guard” the hydroprocessing reactor 204. The Guard bed 202 is also configured to remove metals, such as zinc, potassium, and phosphorous, by physical means such as adsorption.

[0094] The catalyst in the guard bed 202 may be nickel (Ni) or vanadium (V) or a combination thereof.

[0095] The guard bed 202 may be operated at temperatures from 325 to 400 °C (615 to 750 °F). The temperature in line 214 may be controlled by the heat exchanger 201 to meet the optimal temperature guidelines provided by the catalyst manufacturer.

[0096] The heat exchanger 203 is configured to heat or cool the output stream from the guard bed 202.

[0097] The hydroprocessing reactor 204 may include three stacked or superimposed sections. Each section may have a top zone, a catalytic bed, and a bottom zone. A hydroprocessing catalyst is provided in each of the catalytic beds.

[0098] The hydroprocessing catalyst may be nickel-molybdenum, cobalt-molybdenum, nickel-tungsten, or similar single or mixed metal catalysts. The hydrogen reactor may be operated at temperatures 330 to 405 °C (625 to 760 °F) in the reaction zones.

[0099] The hydroprocessing catalyst may also include any other suitable catalysts for hydroprocessing treatment and may be obtained from commercial sources or chemical suppliers. For example, the hydrogen catalyst may be an inert material, including a precious metal such as palladium, platinum, or the like. The catalyst promotes reaction of hydrogen with other molecules, such as with unsaturated hydrocarbons to form saturates, with sulfur to form H2S, and with nitrogen to form NH3.

[0100] During operation, the distillate stream from the CSU 10’, which containspurified vacuum gas oil (VGO), is heated by heat exchanger 201 before being introduced into the guard bed 202 through line 214. Hydrogen is also added to the guard bed through lines 212, 213, and 214. The temperature of the stream flowing through line 214 may be controlled to be in the range of 325 to 400 °C (615 to 750 °F) depending on the desired operating temperature in the guard bed 202.

[0101] The liquid mixture in line 214 is then introduced into the guard bed 202. The guard bed 202 removes certain targeted contaminants present in the purified used oil stream from CSU 10’, which contaminants might otherwise poison the hydroprocessing catalyst in the hydroprocessing reactor 204, and lower the lifetime of the hydroprocessing catalyst. For example, metal elements and other materials may be removed in the guard bed 202 to protect the catalyst in the hydroprocessing reactor 204.

[0102] It is expected that in both guard bed 202, and the hydroprocessing reactor 204, the reactions with hydrogen will break some double bonded molecules, such as olefins, aromatics, naphthenic and cyclic components to produce more paraffinic compounds. At the same time, some impurities such as compounds containing sulfur or nitrogen can react with hydrogen to form bonds between hydrogen and sulfur or nitrogen atoms. Some of these sulfur and nitrogen-containing molecules are converted to gases, such as ammonia and sulfur gases of various type (e.g., hydrogen sulfide). These gases can be vented from the guard bed 202 or reactor 204 to an appropriate collection and treatment system (not shown).

[0103] The output from the guard bed 202 is a liquid mixture. The liquid mixture is transported from the guard bed 202 to heat exchanger 203 through transport line 215.The heat exchanger 203 either heats or cools the liquid mixture depending on the required temperature for the reactions in hydroprocessing reactor 204. The temperature of the stream through line 215 may be controlled to be in the range of 330 to 405 °C (625 to 760 °F) depending on the desired operating temperature in the hydroprocessing reactor 204.

[0104] Hydrogen is continuously added to the liquid mixture through the hydrogeninlet 218, via lines 212 and 217. The hydrogen may be added under a constant pressure so the amount of the hydrogen added is stable over time.

[0105] A portion of the output stream in line 222 is also added to the liquid mixture through lines 223, 217, and inlet 218. With the recycled outstream from line 222, which can function as a diluent, the added hydrogen can be more quickly dissolved in the liquid mixture, and the liquid mixture can contain a higher concentration of hydrogen. As a result, most added hydrogen could be in the liquid phase when the mixture is introduced into the hydroprocessing reactor 204.

[0106] The mixture introduced into the hydroprocessing reactor 204 undergoes hydroprocessing reactions with hydrogen in the presence of the hydroprocessing catalyst.

[0107] Hydro processing catalysts include base metal and noble metal catalysts on a support appropriate to perform the desired hydroprocessing transformation.Hydrotreating catalysts saturate carbon-carbon double bonds and desulfurize and denitrogenize the feedstock (VGO). Hydroisomerization catalysts convert linear paraffinic molecules into branched chain molecules. Hydrocracking catalysts cause ring opening reactions that convert naphthenic molecules into paraffinic molecules thus increasing the Viscosity Index of the feedstock. Combinations of these catalysts in series in the same reactor or in separate reactors may be advantageous in conversion of feedstock into higher VI product with the desired qualities of a Group III base oil.

[0108] In some embodiments, the hydroprocessing reactor may saturate double bonds, desulfurize feedstock, denitrogenize feedstock, convert linear paraffinic compounds into branched chain molecules, and cause ring opening reactions.

[0109] The hydroprocessing catalyst in the reactor 204 may be completely wetted constantly due to over saturation of hydrogen in the base oil.

[0110] In addition to adding hydrogen and the recycled output portion at thehydrogen inlet 218, the mixture of hydrogen and the recycled output portion in line 217 may also be added at one or more other inlets, such as input ports 219 and 220, of the hydroprocessing reactor 204, arranged along a length over different reaction zones in the reactor 204.

[0111] The reaction zones in the hydroprocessing reactor 204 may be pressurized, such as to a typical pressure of 35 atm (3545 kPa or 515 psi) to 200 atm (20265 kPa or 2940 psi), and heated to a suitable elevated temperature. The hydroprocessing reactor catalyst is selected to promote certain reactions over others, so the reactions in the hydroprocessing reactor 204 are selective in favor of reactions involving molecules with lower lubrication values or properties, such as unsaturated hydrocarbons or non-saturates.

[0112] In the hydroprocessing reactor 204, unsaturated hydrocarbons, olefins, elemental contaminants such as sulfur, nitrogen, oxygen, heteroatoms, and the like that are present in the feed stream are hydrogenated. Some of the reaction products are gases, which are vented through various gas outlets (not shown) at the top portions of the respective catalyst sections. As a result, the output product extracted from the hydroprocessing reactor 204 through output line 222 has an increased level of saturates, a decreased level of contaminants including sulfur, and decreased level of aromatics, and has an increased viscosity index.

[0113] The output liquid stream from reactor 204 is further treated in MSU 30’.

[0114] The output streams from the MTU 20’ may have a higher concentration of saturated hydrocarbons and volatile compounds of hydrogen.

[0115] A portion of the output stream from the reactor 204 may be recycled back to the reactor 204 through line 223, and inlet 218 and input port 221 , as depicted in FIG. 2. The recycled stream could provide at least a portion of the needed hydrogen to the reactor 204, and may also function as a heat sink, thus further reducing temperature fluctuations in the reactor 204. The treatment process in reactor 204 can thus be more isothermal.

[0116] Flow control devices such as valves, flow meters, or pumps (not shown for simplicity and easier viewing) may be provided in lines 222 and 223 to control and adjust the flow rates in these lines as can be understood by those skilled in the art. A typical recycle rate of the output stream to recycled feed may be 5:1 . Recycling in this manner is also beneficial when there is temporary suspension of incoming feed from CSU 10’ or temporary suspension of operation in MSU 30’, as the MTU 20’ could continue to run using the recycled feed at a relatively low feed rate with reduced risk of coking and associated plugging in the MTU 20’. A pump (not shown) may be used to recycle the recycle stream from reactor 204 to inlet 221 . Conveniently, the recycled stream is an inert hydrogen carrier.

[0117] Make-up hydrogen may be added to the liquid mixture containing the recycled stream through line 212 and 217, by feeding the make-up hydrogen into the system through the hydrogen inlet 218, for example. A gas compressor (not shown) may be used to compress the hydrogen gas to be added.

[0118] In some embodiments, excess hydrogen may be added and mixed with liquid mixture in line 214 or 221 so that the resulting liquid mixture contains the maximum amount or concentration of hydrogen in the liquid phase, which would increase reaction performance. Some of the added hydrogen may remain in the gas phase when the added hydrogen is in excess of the maximum amount soluble in the given liquid mixture.

[0119] The hydroprocessing reaction conditions can be selected so that sufficient hydrogen is provided in the liquid phase to accelerate the hydroprocessing reaction or maximize / optimize the reaction performance.

[0120] As now can be appreciated, the entire output stream from line 118 of the CSU 10’ is fed to the MTU 20’, and only a small portion containing impurities is removed by guard bed 202. As a result, a relatively larger portion of the physically purified stream from line 118 flows through the hydroprocessing reactor 204. By comparison, in a system where the solvent treatment section is downstream of the hydroprocessing section (seee.g. US8366912, where Zone 50 is the solvent treatment section and Zone 60 is hydroprocessing section), only the base oil portion extracted from the extract stream from the MSU is fed to the hydroprocessing reactor, which is a relatively smaller portion of the output stream from the CSU (e.g., distillate outlet 118 in US8366912). That is, a significantly smaller portion of the distillate output flows through the hydroprocessing reactor at a significantly lower volumetric flow rate.

[0121] Many of the hydroprocessing reactions that may occur in the reactor 204 are exothermic, and can thus potentially cause temperature in the reactor to drift or fluctuate depending on the reaction rates and conditions of the catalyst and the availability of hydrogen. In an embodiment described herein, when the fluid flow rate is high, particularly with the recycled portion and the increased input from the CSU, the temperature in the hydroprocessing reactor 204 can be more stable, because the temperature is mainly dependent on the temperature of the input liquid mixture, and any temperature fluctuation caused by the heat generated by the hydroprocessing reaction is relatively minor. The hydroprocessing process may be considered to be generally isothermal.

[0122] As used herein, “runaway reactions” refer to thermally unstable reactions, which may occur in the reactor, exhibiting uncontrolled accelerating rates of reaction leading to rapid increases in temperature (e.g. in localized zones), and possibly pressure, in the reactor. “Hot spots” refer to localized zones in which the local temperatures are substantially higher than the temperatures in the neighboring zones, and higher than the normal operating temperatures for the reactor.

[0123] To further offset any heating effect or to better control the temperature in the system, the heat exchanger 203 may be used to adjust the input temperature, such as to cool the liquid mixture passing through lines 216 and 221.

[0124] It is also expected that with the MTU 20’, less stringent operation control may be possible, as compared to conventional base oil upgrading systems.

[0125] Hydroprocessing reactor 204 may be equipped with one or more hydroprocessing catalysts with metal components from Groups V(b), Vl(b) and VIII of the Periodic Table, as known to those skilled in the art. In some embodiments, compounds of nickel, molybdenum, vanadium, tungsten, or cobalt metal supported on carriers, such as activated carbon, kieselguhr, silica, alumina and the like, e.g., cobalt-molybdenum on alumina, nickel-molybdenum on alumina, or nickel-tungsten on silica / alumina, may be used.

[0126] In a particular embodiment, the hydroprocessing catalyst may be a nickelmolybdenum, cobalt-molybdenum, nickel-tungsten or similar single or mixed metal catalysts.

[0127] An embodiment of the MTU described herein may be operated for continuous flow, but may also be operated in the batch mode if desired.

[0128] Metals, phosphorus, silicon, and long chain polymers present in the feedstock may remain in the output of purified used oil stream from vessel 112, which if allowed into the hydroprocessing reactor could deactivate the catalyst and cause fouling, particularly at lower flow rates in a gas phase trickle bed hydroprocessing reactor. In embodiments described herein, such downsides and problems may be reduced or avoided by using the guard bed 202.

[0129] The catalyst may be selected to remove or convert undesired chemical components, such as aromatics, olefins, nitrogen, sulfur, or the like. Some of these compounds may be reacted or converted into stable chemical compounds in the presence of hydrogen. Unsaturated aromatics and olefins may become saturated in the reactor 204.

[0130] Further, recycling a portion of the output stream in the hydroprocessing reactor 204 allows more efficient use of hydrogen to keep excess hydrogen in the reaction zone in the reactor. The recycled stream may also act as a heat sink to maintain more uniform and stable temperature in the reactor, thus allowing better temperature control,and reduces the risk of coking in the reactor. The hydroprocessing reactor as described herein may be readily configured and adapted to accommodate changes in the feedstock or input used oils.

[0131] In some embodiments, a continuous flow liquid phase hydroprocessing step may be conducted in a reactor at a predetermined temperature, and having an upper zone of gases and a substantially larger lower zone of hydrogen dissolved in a mixture of liquids surrounding the catalyst.

[0132] The MSU 30’ includes a heat exchanger 301 at a transport line 322 connected to the line 222, an extraction column 302, a solvent source or system (not shown) for supplying a solvent through line 312, a flash drum, vessel 303, a heat exchanger 304, a solvent separation vessel 305, and a heat exchanger 306. The MSU 30’ also includes transport lines 311 , 313, 314, 315, and 316 interconnecting the other components discussed above and output line 317 for outputting the base oil product from vessel 305. The extraction column 302 may be an agitated counter-current liquid-liquid extraction column.

[0133] The heat exchanger 301 may be configured and positioned to heat the output stream from the MTU 20’, particularly the reactor 204, before this chemically treated stream is introduced into the solvent extraction column 302 through line 311.

[0134] The solvent extraction column 302 has a bottom, a top, a contact section between the bottom and the top, an inlet connected to the transport line 312 for introducing an extraction solvent into the solvent extraction column 302, a top outlet connected to the transport line 313, and a bottom outlet connected to the line 316.

[0135] The solvent extraction column 302 also includes agitation motor (M) for actuating a variable speed agitator (not separately shown) in the column 302 configured and operable to agitate the chemically treated stream and the extraction solvent flowing in the solvent extraction column 302, at a variable agitation speed. The agitation speed couldbe controlled independent of the flow rates of the fluids in the solvent extraction column 302. The agitator may be a rotary agitator, reciprocal agitator, pulsed agitator, or the like. The solvent extraction column 302 may be similar to the solvent extraction column described in US20220089968, the contents of which related to the solvent extraction column and the extraction solvent are incorporated herein by reference.

[0136] Outputs from the solvent extraction column 302 include a first liquid phase, which is the lighter phase, a second liquid phase, which is the heavier phase. For example, when the extraction solvent is NMP and the chemically treated stream includes base oils that are lighter than NMP, the NMP solvent is the heavier phase and will be introduced into the column through the top inlet and line 312, and the chemically treated stream will be introduced into the column 302 through the lower inlet and line 311 , as illustrated in FIG. 2.

[0137] The extraction solvent may be NMP and may be stored in a solvent storage or solvent system. The solvent is supplied to the solvent extraction column 302 through line 312.

[0138] The vessel 303 is connected to the solvent extraction column 302 through line 313 to receive the light phase (the raffinate stream) output from the solvent extraction column 302, and connected to the solvent separation vessel 305, which may use steam stripping, through heat exchanger 304 and lines 314, 315 for separating and recovery of the extraction solvent from base oil products. The recovered solvent may be optionally recycled and feed back to the solvent source or solvent system (not shown). The separated oil portion from the raffinate is output from vessel 305 through line 317 as an oil product, which contains HQBO, such as Group III base oils.

[0139] An additional advantage of the use of hydroprocessing the VGO prior to extraction is that the extraction process has less undesirable components to process leading to a more efficient and effective extraction of the lower quality base oil components from the desired Group III base oil fraction.

[0140] The extract stream from the solvent extraction column 302 is fed as input to the extract treatment unit 40’ for further treatment as will be described below.

[0141] In operation, the chemically treated used oil stream is passed through the heat exchanger 301 and line 311 to the solvent extraction column 302 as the feed for the solvent extraction process. The feed is driven (such as by a pump, not shown) to flow upward forming an upward current in the contact section of the column 302. The extraction solvent provided from the line 312 is introduced to the top inlet of the solvent extraction column 302 and is driven to flow downward forming a downward current in the contact section. The extraction solvent and the feed thus come into contact as counter currents. The extraction temperature in the contact section is maintained at a temperature below the threshold temperature at which the extraction solvent and the oil components in the feedstock become completely miscible. For example, when NMP is used, optionally with a low concentration of water (e.g. up to 1 vol%), the extraction temperature may be in the range of about 38 °C (100 °F ) to about 66 °C (150 °F). The volume ratio of the extraction solvent to the feed may be from about 1 to about 4, depending on the quality and properties of the feed and the selected flow rates. Compounds in the feed that are soluble in the extraction solvent at the extraction temperature are dissolved and dispersed in the extraction solvent and thus separated from compounds in the feedstock that have a lower solubility or insoluble in the extraction solvent at the extraction temperature. The dissolved compounds are extracts, as they are “extracted” by the solvent. The nondissolved and un-extracted compounds, commonly referred to as the raffinate, and are output as the raffinate stream through line 313 to the vessel 303 and then vessel 305 through lines 314 and 315. The raffinate stream may also contain a small portion of the extraction solvent (such as less than 10 vol%).

[0142] The ratio of the flow rate of the extraction solvent to the flow rate of the feed may be adjusted depending on the oil quality in the feed. For example, the flow rates may be adjusted so that the solvent to feed ratio in the contact section may be from about 1 to about 4.

[0143] The agitation speed in the solvent extraction column can be controlled and adjusted without affecting the flow rates, using a variable speed agitator. The agitation speed may be selected and controlled based on the quality and properties of the feedstock and the selected flow rates.

[0144] The contact section in column 302 may be heated so that the desired extracts will have sufficiently high solubility to dissolve and disperse in the extract stream containing the extraction solvent. The temperature should not be too high so that selected hydrocarbons will not dissolve in the extraction solvent and will remain in the raffinate stream.

[0145] The temperature in the solvent extraction column may be selected and controlled based on the quality and properties of the feed, according to known technology or knowledge. Even when the flow rates are slow, the feed and the extraction solvent can be sufficiently and quickly mixed for contact by the agitator. The variable speed agitator thus provides increased efficiency and allows convenient control and adjustment to accommodate possible variations in the feed.

[0146] Further, due to the increased content of saturates and decreased content of polar molecules in the chemically treated stream in the feed, the extraction efficiency in column 302 can be improved, resulting in an increased product yield.

[0147] The raffinate stream may include a higher quality base oil. The raffinate stream is transported from the top of solvent extraction column 302 to vessels 303 and then 305. The higher quality base oil may be separated from the residual extraction solvent in vessel 305, such as by heating to a temperature above the boiling point of the solvent and below the boiling point of the base oil. The separated solvent may be returned or recycled. The bottom stream from vessel 305 is output as the base oil product as discussed above, which contains HQBO including Group III base oils.

[0148] The extract stream includes the extraction solvent and the extractedcompounds (extract), moves downward, and is output through line 316 to the extract treatment unit 40’. The compounds dissolved or dispersed in the solvent typically include some base oils, which may be of lower quality as compared to the base oils in the raffinate stream.

[0149] The extract treatment unit 40’ includes a distillation column 401 connected to the solvent extraction column 302 by line 316, a reflux condenser 402 and a reflux drum 403 connected with the top of the column 401 by lines 411 , 412, and 413 forming a closed loop.

[0150] The extract treatment unit 40’ also includes reboiler 404 connected to the outlet line 414 of the distillation column 401 .

[0151] A portion of the output stream from reboiler 404 is fed back to the distillation column 401 though lines 415, 416 and the other portion of the output stream is supplied to the distillation column 405 through lines 415 and 417.

[0152] The distillation column 405 is configured to separate the extraction solvent from the base oil components in the extract stream, and thus recover the solvent from the top of the distillation column 405 and produce a base oil stream at the bottom of distillation column at outlet 406. The base oil product passes through a heat exchanger 406 and may be transported for further processing, such as stripping.

[0153] During operation, the extract stream from solvent extraction column 302 is fed into distillation column 401.

[0154] It can be understood that the extract from column 302 can contain the extraction solvent, some light petroleum materials, and certain lube oil components. The distillation column 401 is configured and used to remove the extraction solvent.

[0155] Distillation column 401 and the reflux condenser 402 and reflux drum 403 can be operated in a conventional manner to remove the overhead materials, whilerecycling some of the heavier materials back to the distillation column through line 413.

[0156] The bottom output from column 401 contains the solvent and some base oil components, such as Group II / II+, and is further treated in distillation column 405 after passing through reboiler 404 to vaporize and recycle some light portions of the bottom output back to the column 401 through inlet line 416. The distillation column 405 may include steam stripping.

[0157] The reboiler 404 may also be configured and operated according to a conventional technique. The light materials vaporized by reboiler 404 may rise to the top of column 401 and be processed in the reflux devices.

[0158] Distillation column 405 may be configured and operated according to a conventional technique for solvent recovery with steam stripping capability.

[0159] Conveniently, after the solvent is separated and recovered in column 405, the remaining bottom output contains useful base oil products including Group II / II+ base oils.

[0160] The oil products produced by the system shown in FIG. 2 contains upgraded oils, which may contain at least 90 wt% of saturates and less than 0.03% sulfur, and have a viscosity index of at least 80. The saturate level in the oil product may be higher than 95 wt%. The VI of the oil product may be higher than 120, such as 125. The oil product may be suitable for use as base oil under Group II or III of API 1509.

[0161] Various modifications and improvements may be made in the system of FIG. 2.

[0162] For example, it may be desirable in some instances to chemically treat the used oil feed with a base or alkali material such as sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium hydroxide, or the like. Such treatment can condition, stabilize, or otherwise neutralize the used oil to reduce the risk of fouling in the system, tofacilitate separation of the used oil stream into constituent parts, or to enhance the quality of any non-base oil by-products.

[0163] In some instances, it may also be desirable to add an alkali or base to one or more of the distillation vessels either in the feed stream, recycle stream or directly into the vessel(s).

[0164] In the embodiment described above, four distillation vessels are used to separate a base oil fraction from other constituents in the used oil. However, in different embodiments, fewer, such as two or three, distillation vessels, or more, such as eight, distillation vessels, may be used in the CSU to purify the oil feed.

[0165] In the embodiment described above, the distillation vessels may be flash vessels. The physical separate unit may include any device or system that can purify the used oil feed, and may include single stage separation / purification devices, such as evaporators, thin or wiped film evaporators, columns, vessels, tanks, pipes, and the like.

[0166] In the embodiment described above, steam or a gas may be added to distillation vessels 52, 70, 90 and 112 to help strip tight distillates from the used oil thereby enhancing separation / purification.

[0167] Steam stripping is a technique known to those skilled in the art for enhancing distillation processes, and may be utilized in system 5.

[0168] It may be desirable in some instances to add the stream recovered through line 96, which has a boiling range typically from about 260 °C (500 °F) to about 350 °C (660 °F) (i.e. gas oil) to the stream in line 118 for chemical treatment in the MTU 201 since this stream may also be suitable for use as a base oil, and will further increase the flow rate through hydroprocessing reactor 204, thus allowing a larger size reactor.

[0169] For the specific embodiment shown in FIG. 2 described above, the extraction solvent has a specific gravity greater than the base oils in the feed, so that thecountercurrents can be formed in the directions as described and illustrated in FIG. 2.However, in different embodiments, an extraction solvent may have a specific gravity less than the base oils to be produced, the process and system may be correspondingly modified to reverse the current flow directions of the solvent and the feed. That is, the solvent may be introduced into the bottom of the solvent extraction column and the feed may be introduced into the top of the solvent extraction column.

[0170] While FIG. 2 shows one guard bed 202, and one hydroprocessing reactor 204, in different embodiments, two or more guard beds, configured in series or in parallel, can be used upstream of the hydroprocessing reactor 204. The guard beds in parallel can be operated one at a time to enable regeneration or clean out and recharging of one of the guard beds without interrupting the flow to reactor 204.

[0171] Similarly, more than one hydroprocessing reactors may be operated in series to enhance operation.

[0172] In the embodiment described above it may be possible to incorporate a hydrogen recovery system to recover hydrogen from the product stream in line 222. The hydrogen recovery system can purify and recover the hydrogen in this stream and recycle it back for use through the line 212.

[0173] It may also be desirable to employ steam or gas stripping to remove nonbase oil light contaminates from the base oil products. An additional vessel may also be added to further process the base oil products by further fractionating the base oil product to form different products with different viscosities, or stripping the base oil products to reduce its volatility.

[0174] Steam stripping may be utilized to reduce the vapor pressure at a selected location in the system. With reduced vapor pressure, the operation temperature may also be lowered, and thus reducing the heating energy required to maintain operation and the risk of fouling. Steam stripping may also assist to enhance yield and quality of useful oilproducts.

[0175] The solvent extraction column 302 may be any suitable agitated continuous flow liquid phase extraction column where the agitation speed is variable and can be controlled. The extraction solvent may be selected from ethanol, diacetone-alcohol, ethylene-glycol-mono(low alkyl)ether, di-ethylene-glycol, diethylene-glycol-mono(low alkyl)ether, o-chlorophenol furfural, acetone, formic acid, 4-butyrotacetone, low alkyl-ester of low mono- and dicarbonic acids, dimethylformamide, 2-pyrrolidone and N-(low alkyl)-2- pyrrolidone, N-methyl-2-pyrrolidone (NMP), epi-chlorohydrin, dioxane, morpholine, low- alkyl and amino(low-alkyl)morpholine, benzonitrile or di-low-alkyl)sulfoxide, and phosphonate, or the like.

[0176] Temperature gradients or regional heating or cooling can be used at various points on the feed line or across the solvent extraction column 302 to effect performance and selectivity. Recycling of the raffinate and an extract at similar or different temperatures can also be employed. In some instances it may be beneficial to remove a side stream from the extraction column, to cool the raffinate or extract streams, to cool the side stream, and to separate a portion of the solvent from the oil product stream and return the separated oils to the extraction column 302.

[0177] The distillation in the MSU 30’ and extract treatment unit 40’ can be undertaken atmospherically or under vacuum. One or more flash separators, vacuum separators, multistage columns, or the like, or combinations thereof either operated atmospherically, or under pressure or vacuum, can be used in order to separate the solvent from the base oils.

[0178] In some embodiments, additional processing may be undertaken on the distillate stream in line 54 such as further separating the constituents of this stream such as water, glycols, solvents, light hydrocarbons, and the like, thereby creating separate products which may be used or further upgraded to higher quality products. These product streams may also be further treated to improve their quality as known to those skilled inthe art.

[0179] A continuous flow liquid phase hydroprocessing process can provide a continuous surplus of hydrogen in the reaction zone during hydroprocessing reactions, which can conveniently prevent or reduce catalyst coking. In addition, the continuous flow liquid phase hydroprocessing process does not use trickle beds, thereby avoiding the problem of fouling in conventional trickle bed reactors, typically used in re-refineries.

[0180] Performing continuous flow liquid phase hydroprocessing upstream of the solvent extraction process also conveniently allows better control of the heat and temperature distribution and fluctuation inside the hydroprocessing reactor and helps in maintaining a steady or stable temperature inside the reactor, thereby minimizing the need for multiple catalyst beds and large amount of hydrogen gas to quench the reactor.

[0181] It is noted that used oils can contain sludge and long-chain polymers, which may be formed due to usage and degradation of the engine oil or motor oil during use, or during the re-refining process. The presence of these sludge and long chain polymers could cause fouling and affect the run length of treatment processes at various stages. In an embodiment as disclosed herein, these materials may be effectively managed and removed, thus reducing the risk of fouling and prolong the run length of the treatment processes. For example, fouling in the CSU may be reduced by reducing internal surfaces in the distillation vessels, reducing rotating equipment, increasing flow rate, or reducing operation temperatures, or combinations thereof. Recirculation of residuals also helps to maintain higher flow rates. Using staged distillation in flash and vacuum distillation vessels, instead of thin-film evaporators (TFE), could allow sequential removal of physical contaminants with more efficient separation and increased yields of quality VGO, and reduced fouling. Thus, a wider range of UMO feedstocks may be suitable for processing in an embodiment disclosed herein, as compared to a conventional re-refining system. An embodiment of the CSU as disclosed herein may have a long on-stream run time, such as more than 6 months.

[0182] It may also be noted that pretreating the purified used oil by hydroprocessing before the solvent treatment may reduce the amounts of fluids to be treated by solvent exchange, which may reduce the amount of solvent used and improve solvent treatment efficiency.

[0183] It is noted that the saturate and sulfur levels and VI of base oils indicated herein are measured using the tests and analytical methods specified in API 1509, Table E-1. Specifically, the saturate level is measured according to ASTM International standard, ASTM D2007, the VI is calculated according to ASTM D2270, and the sulfur level is measured according to one or more of ASTM D1552, D2622, D3120, D4294, or D4927.

[0184] As used herein, the term “about” when used with a numerical value indicates that a 10% variation, either above or below the given value, is permissible, unless otherwise specifically indicated.

[0185] It will be understood that any range of values herein is intended to specifically include any intermediate value or sub-range within the given range, and all such intermediate values and sub-ranges are individually and specifically disclosed.

[0186] It will also be understood that the word “a” or “an” is intended to mean “one or more” or “at least one”, and any singular form is intended to include plurals herein.

[0187] It will be further understood that the term “comprise”, including any variation thereof, is intended to be open-ended and means “include, but not limited to,” unless otherwise specifically indicated to the contrary.

[0188] When a list of items is given herein with an “or” before the last item, any one of the listed items or any suitable combination of two or more of the listed items may be selected and used.

[0189] Of course, the above described embodiments of the present disclosure are intended to be illustrative only and in no way limiting. The described embodiments aresusceptible to many modifications of form, arrangement of parts, details, and order of operation. The invention, rather, is intended to encompass all such modification within its scope, as defined by the claims.

Claims

WHAT IS CLAIMED IS:1 . A method of processing used oils to produce base oils, comprising: physically separating contaminants from a feed of used oils to produce a physically- purified stream comprising purified used oils and a stream comprising the contaminants, the physically separating comprising distillation; chemically treating the physically-purified stream to produce a chemically-treated stream comprising chemically-treated used oils, the chemically treating comprising hydroprocessing in a reactor in the presence of a catalyst selected for at least hydrodesulfurization, hydrodenitrogenation and hydrogenation, wherein a first portion of the chemically-treated stream is recycled through the reactor to increase a total volumetric flow rate through the reactor and to reduce hot spots and runaway reactions in the reactor; and contacting a second portion of the chemically-treated stream with an extraction solvent to produce an extract stream and a raffinate stream, the extraction solvent selected to dissolve selected soluble compounds in the chemically-treated stream, wherein the extract stream comprises the extraction solvent and the selected soluble compounds dissolved in the extraction solvent, wherein the hydroprocessing decreases a concentration of polar molecules and increases a concentration of saturates in the chemically-treated stream, and increases a viscosity index of the chemically-treated stream.

2. The method of claim 1 , wherein the raffinate stream comprises a base oil having a viscosity index of greater than 120, a concentration of sulfur of less than 0.03 wt%, and a concentration of saturates higher than 90 wt%.

3. The method of claim 1, wherein the chemically treating comprises adding hydrogen to the physically-purified stream to form a first liquid mixture of the physically-purifiedstream and hydrogen dissolved therein; passing the first liquid mixture through a guard bed comprising a catalyst to remove metal elements and produce a second liquid mixture comprising reduced metal elements; and feeding the second liquid mixture to the reactor to produce the chemically-treated stream.

4. The method of claim 3, wherein the first portion of the chemically-treated stream is added to the second liquid mixture before feeding the second liquid mixture to the reactor.

5. The method of claim 3, wherein a temperature of the first liquid mixture is from 325 °C to 400 °C.

6. The method of claim 3, wherein a temperature of the second liquid mixture is from 330 °C to 405 °C.

7. The method of claim 1 , wherein the extraction solvent is N-Methyl 2-Pyrrolidinone.

8. The method of claim 1 , wherein the second portion of the chemically-treated stream and the extraction solvent are contacted in a continuous flow solvent extraction column.

9. The method of claim 8, wherein the continuous flow solvent extraction column comprises a variable speed agitator.

10. The method of claim 2, further comprising treating the raffinate stream to extract the base oil.11 . The method of claim 10, further comprising treating the extract stream to recover the extraction solvent and produce another base oil.

12. A system for processing used oils to produce base oils, comprising:a physical separation subsystem for physically separating impurities and contaminants from a feed of used oils to produce a physically-purified stream comprising purified used oils and a stream comprising the impurities and contaminants, the physical separation subsystem comprising a plurality of distillation vessels; a chemical treatment subsystem for chemically treating the physically-purified stream to produce a chemically-treated stream comprising chemically-treated used oils, the chemical treatment subsystem comprising a hydroprocessing reactor comprising an inlet connected to the physical separation subsystem, an outlet, and a catalyst selected for at least hydrodesulfurization, hydrodenitrogenation, and hydrogenation, to reduce concentrations of sulfur, nitrogen, and polar molecules and increase concentrations of saturates in the chemically-treated stream, and to increase a viscosity index of the chemically-treated used oils; a conduit connecting the outlet of the hydroprocessing reactor to the inlet of the hydroprocessing reactor, for recycling a first portion of the chemically-treated stream through the hydroprocessing reactor to increase a total volumetric flow rate through the hydroprocessing reactor and to reduce hot spots and runaway reactions in the hydroprocessing reactor; and a solvent extraction column connected to the outlet of the hydroprocessing reactor for receiving and contacting a second portion of the chemically-treated stream with an extraction solvent to produce an extract stream and a raffinate stream, the extraction solvent selected to dissolve selected soluble compounds in the chemically-treated stream, wherein the extract stream comprises the extraction solvent and the selected soluble compounds dissolved in the extraction solvent, and the raffinate stream comprises a base oil having a viscosity index of greater than 120, a concentration of sulfur of less than 0.03 wt%, and a concentration of saturates higher than 90 wt%.

3. The system of claim 12, wherein the hydroprocessing reactor is configured and the catalyst is selected to convert linear paraffinic compounds to branched chainmolecules and cause ring opening reactions.

14. The system of claim 12, wherein the chemical treatment subsystem comprises a hydrogen source for adding hydrogen to the physically-purified stream to form a first liquid mixture, a guard bed comprising a catalyst disposed downstream of the distillation vessels and upstream of the hydroprocessing reactor, for removing metal elements from the first liquid mixture and producing a second liquid mixture comprising reduced metal elements; and a conduit connecting the guard bed to the inlet of the hydroprocessing reactor to feed the second liquid mixture to the hydroprocessing reactor.

15. The system of claim 12, wherein the catalyst comprises a nickel-molybdenum, cobaltmolybdenum, or nickel-tungsten catalyst.

16. The system of claim 12, wherein the catalyst comprises a metal catalyst comprising one or more metal elements.

17. The system of claim 12, wherein the hdyroconversion reactor is configured to operate at a temperature of 330 °C to 405 °C.

18. The system of claim 14, wherein the guard bed comprises a nickel or vanadium catalyst and is configured to operate at a temperature of 325 °C to 400 °C.

19. The system of claim 12, wherein the solvent extraction column comprises a variable speed agitator.

20. The system of claim 12, comprising a recovery subsystem for recovering the extraction solvent from the extract stream and for recovering a further base oil from the extract stream.

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