Method and system for re-refining and upgrading used oil

Abstract

To provide a method for re-refining used oil.SOLUTION: A method for re-refining used oil includes executing continuous liquid-liquid solvent extraction by contacting a feedstock containing refined used oil with an extraction solvent, and generating an extract stream including the extraction solvent and an extract dissolved in the extraction solvent. The feedstock and the extraction solvent are stirred by a variable-speed stirrer at a selected stirring speed during the solvent extraction. The extract is separated from the extraction solvent and undergoes continuous-flow liquid-phase hydrotreating to produce an oil product. A system for executing the method includes a refining apparatus for refining the used oil, an extraction column for extracting the extract from the feedstock, and a continuous-flow liquid-phase hydrotreating apparatus. The extraction column includes a stirrer configured to stir the feedstock and the extraction solvent passing through the extraction column at a variable stirring speed.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Cross - reference to Related Applications This application claims the benefit and priority of European Patent Application No. 19155542.4, titled "Method for Producing High Quality Base Oil from Waste Oil", filed on February 5, 2019, the entire content of which is incorporated herein by reference.

[0002] The present disclosure generally relates to methods for the re - refining or upgrading of used oils.

Background Art

[0003] Used oils, including waste oils, can be re - refined or upgraded to produce useful base oils, fuel oils, and other oil products or by - products. Base oils are also referred to as base stock, base lube stock, lube stock, lube oil, or lubricating oil, etc. By using base oils, products having lubricating properties such as lubricating oils, metal - working oils, or hydraulic oils can be manufactured.

[0004] Base oils can be produced by refining crude oils such as paraffinic crude oil or naphthenic crude oil using various processing technologies and equipment. For example, crude oil can be subjected to heating and distillation processes to separate light and heavy hydrocarbons, and the heavy hydrocarbons can be further hydrogenated to remove sulfur and aromatic substances, thus producing base oils having a higher ratio of saturates, a lower sulfur content, and a higher viscosity. The light hydrocarbons produced in these processes can be used as fuel oils.

[0005] Base oils produced by refining crude oil are officially classified into various groups by the American Petroleum Institute (API). According to the current API classification (API 1509), Groups I, II, and III are classified based on physical properties and compositional characteristics. Specifically, Groups I, II, and III are characterized and distinguished mainly by their saturation levels, sulfur levels, and viscosity index (VI). The saturation level and sulfur level can be indicated by the percentage of saturated substances and sulfur in the oil. The viscosity index is a measure of the change in viscosity with temperature, typically measured at 100°F (40°C) and 210°F (100°C). Base oils with higher saturation levels, lower sulfur levels, and higher viscosity indices are considered high-quality base oils. For example, according to the current API classification (API 1509), Group I base oils have less than 90% saturated substances and / or more than 0.03% sulfur, and a VI (viscosity index) of at least 80 and less than 120. Group II base oils have at least 90% saturated substances and a maximum of 0.03% sulfur, but the VI is still at least 80 and less than 120. Group III base oils have at least 90% saturated substances, a maximum of 0.03% sulfur, and a VI of at least 120. All percentages in this specification are mass percentages (denoted as wt%) based on the total mass of the oil product, including any impurities and additives, unless otherwise specified.

[0006] Group II and Group III base oils can be considered high-quality base oils, and base oils that do not meet any of the Group I, Group II, and Group III standards are considered low-quality base oils.

[0007] In the processing of conventional refineries, typically, Group I base oils can be produced after a solvent refining process. Group II base oils can be produced after mild hydrotreating or hydrocracking. Group III base oils can be produced by more extensive hydrocracking or catalytic dewaxing.

[0008] It is also possible to re-refine used oil such as used motor oil (UMO) to produce high-quality base oils such as Group I, II, or III base oils. For example, systems and methods for producing Group II or III base oils and other products from used oil have been proposed, which involve subjecting the used oil to distillation, solvent exchange in a packed extraction column, and vapor-phase hydrogenation treatment. See, for example, WO2006 / 096396 published on September 14, 2006, and US8,366,912 issued on February 5, 2013. The technology for re-refining used oil is also disclosed in US6,117,309 issued on September 12, 2000.

[0009] However, there is still a desire to improve the conventional systems and methods for producing high-quality oil from used motor oil or other used oil.

Summary of the Invention

Problems to be Solved by the Invention

[0010] The inventors have found that the systems and methods for re-refining used motor oil disclosed so far to produce high-quality base oils and other products can be improved to be more robust and convenient, or more efficient, for accommodating various types of feed stocks to be input.

[0011] For example, used oils from various sources of origin can have different contents as well as components and properties. In particular, used oils are collected by waste oil collectors in a number of regions collected from local places of use or manufacturing sites. In the collection process, various oils formulated for a number of types of services can be mixed to form a composite material of different types and different qualities of base oils, chemicals, and contaminants. Therefore, it is considered desirable to provide a system and process that can be conveniently adjusted during the operation of effectively and efficiently treating different feedstock oils having very different components and properties. It is also desirable to improve the yield of useful products recovered from used oils, particularly high-quality base oils such as Group III base oils. It is further desirable to improve the processing capacity of such processes.

[0012] Due to the nature of the collected used oils as considered elsewhere in this specification, in known processes for re-refining waste oils, it is difficult to achieve both high yields and high-quality products. Since the feedstock can include a wide variety of oil types, qualities, and contaminants, existing processes are typically designed to trade off between the two because it is considered difficult to achieve both quality and quantity in these processes. Further, when new types of feedstock are used, existing systems or processes are considered to have to be reconfigured or operated using new operating parameters to optimize the process. Such optimization is considered to require extensive experience, testing, and strict compliance with the optimized operating parameters. Deviation from the optimized operating process or parameters can result in one or more of a decrease in product quality, system failure, shortening of the execution time, decrease in manufacturing efficiency or production yield, or increase in operating costs. For example, if the process is not optimized for a particular application or is deviated from the optimized operating parameters, the lifespan of the catalyst used in this process can be shortened.

Means for Solving the Problems

[0013] Accordingly, aspects of the present disclosure involve contacting a feedstock comprising purified used oil with an extraction solvent to perform continuous liquid-liquid solvent extraction, producing an extract stream comprising the extraction solvent and the extract dissolved therein, wherein the feedstock and the extraction solvent are agitated by a variable speed agitator during solvent extraction at a selected agitation speed, separating the extract from the extraction solvent, and subjecting the extract to continuous flow liquid phase hydrogenation treatment to produce an oil product having a viscosity index of at least 80.

[0014] In the method of the foregoing paragraph, the liquid-phase hydrogenation treatment may include adding a diluent to the extract to enhance the solubility of hydrogen in the extract, thus forming a liquid mixture containing the diluent and the extract; adding hydrogen to the liquid mixture to dissolve the hydrogen in the liquid mixture; heating the liquid mixture having the dissolved hydrogen in the presence of a hydrogenation catalyst to saturate the unsaturated substances in the liquid mixture and removing sulfur and aromatic substances from the liquid mixture, thus forming an oil product. The extract may contain phosphorus and silicon, and the continuous-flow liquid-phase hydrogenation treatment may include removing phosphorus and silicon from the liquid mixture before exposing the liquid mixture to the hydrogenation catalyst. The extract may contain aromatic substances, and the continuous-flow liquid-phase hydrogenation treatment may include removing the aromatic substances from the oil product. The extraction solvent may include n-methyl-2-pyrrolidone. The oil product may contain at least 90 wt% saturated substances, for example, at least 95 wt% saturated substances. The oil product may contain less than 0.03 wt% sulfur. The oil product may have a viscosity index of at least 120. The used oil may include used motor oil or used industrial oil or both. The used oil can be refined to produce a feedstock. The refining of the used oil may include distilling the used oil to form a feedstock containing the distillate from the distillation. The method may include forming a countercurrent flow of the feedstock and the extraction solvent in a solvent extraction column, and the stirring speed and the flow rate of the feedstock and the extraction solvent into the solvent extraction vessel are independently adjusted based on the quality or characteristics of the feedstock.

[0015] In a further aspect, there is provided a system including a refining apparatus configured to refine used oil and form a feedstock including the refined used oil; a continuous countercurrent liquid-liquid extraction column for extracting an extract from the feedstock using an extractant, the extraction column including a stirrer configured to stir the feedstock and the extraction solvent flowing through the entire extraction column at a variable stirring speed; and a continuous-flow liquid-phase hydrogenation apparatus for hydrogenating the extract extracted by the extraction column to produce an oil product.

[0016] In the system of the foregoing paragraph, the continuous-flow liquid-phase hydrogenation apparatus may include a hydrogenation reactor containing a hydrogenation catalyst, a solvent extraction column and a transport line fluidly connected to the hydrogenation reactor for transporting the extract from the solvent extraction column to the hydrogenation reactor, a diluent inlet on the transport line for introducing a diluent into the extract flowing in the transport line to form a liquid mixture containing the extract and the diluent, and a hydrogen inlet on the transport line located downstream of the diluent inlet for introducing hydrogen into the liquid mixture. The liquid-phase hydrogenation apparatus may further include a guard bed located on the transport line between the diluent inlet and the hydrogen inlet, the guard bed being configured to remove at least phosphorus and silicon from the liquid mixture before exposing the liquid mixture to the hydrogenation catalyst. The hydrogenation catalyst may include palladium, gold, or nickel. The purification apparatus may include one or more distillation columns.

[0017] Other aspects, features, and embodiments of the present disclosure will become apparent to those skilled in the art upon a review of the following description of specific embodiments in conjunction with the accompanying drawings.

[0018] By way of example only, in the drawings illustrating embodiments of the present disclosure, it is as follows.

Brief Description of the Drawings

[0019]

Figure 1

[0020]

Figure 2

[0021]

Figure 3

Mode for Carrying Out the Invention

[0022] Briefly, in selected embodiments of the present disclosure, systems and methods are provided for re-refining used motor oil (UMO) or other used oils (including used industrial oils). The systems and methods disclosed herein are modified from previously known systems and methods to enable processing at continuously variable flow rates, particularly low flow rates, and to allow convenient adjustment for accommodating various input feedstocks (including various used oils) that may have substantially different components and properties.

[0023] In some embodiments, the example systems described herein can be conveniently adjusted to process or treat used oils from various sources or various types of oils that require upgrading or refining without the need to interrupt or stop the operation of the system to reconfigure the system. Thus, the exemplary systems can be considered to be more robust and more adaptable.

[0024] In an example embodiment, refined oils such as refined used oil are subjected to stirred solvent extraction and liquid phase hydrogenation. This example system can be conveniently and dynamically adjusted to accommodate various feedstock oils. In particular, the agitation in the solvent extraction stage enables convenient adjustment of the feedstock flow rate. Hydrogenation in the liquid phase also enables convenient adjustment of the processing flow rate. The example system also enables convenient adjustment of other operating parameters, as will be further discussed below.

[0025] Some embodiments of the present disclosure relate to an improved method for producing high-quality base oil from used oil.

[0026] As used herein, the term "used oil" includes any petroleum, or natural or synthetic oil that has been used and as a result may be contaminated with contaminants or impurities and thus has degraded physical or chemical properties. Used oil is typically of lower quality than the original unused oil. Used oil may include waste oil. Used oil may include used motor oil (UMO) or used industrial oil. For example, used oil may include used industrial lubricating oil. UMO can be obtained from various sources such as automobiles, passenger cars, engines, factories, etc. Used oils from different sources may have different properties and components.

[0027] It should be noted that used oil has a composition and properties different from those of crude oil. Crude oil refers to oil extracted from underground oil reservoirs. For example, UMO typically contains contaminants that are not present in crude oil, and the contaminants may include contaminants introduced during the manufacture or use of motor oil, as well as external contaminants such as salts and water. As a result, the processing and treatment technologies for the refining of crude oil and the re-refining of used oil have been very difficult in conventional oil refineries or refining technologies.

[0028] Used oil may include used engine oil. Typically, high-quality base oil is blended with about 30 wt% of functional additives to produce engine oil. These additives often still remain in used engine oil or UMO. Additives may include viscosity modifiers (VM), detergents and dispersants, pour point depressants, anti-wear additives, antioxidants, corrosion inhibitors, metal deactivators, anti-foam additives, or sulfur scavengers, etc.

[0029] VM is typically a long-chain hydrocarbon polymer such as an olefin copolymer, a hydrogenated styrene-butadiene polymer, or a hydrogenated styrene-isoprene copolymer.

[0030] Detergents and dispersants are used in engine oils to maintain combustion by-products dissolved in the base oil. Dispersants are typically long-chain polymers generally derived from poly-isobutene. Detergents typically have an ionic head and a polymeric tail, where the head attracts solids and the tail maintains molecules in solution. Detergents can include, for example, calcium phenate.

[0031] The pour point of the oil is the lowest temperature at which the oil flows. The base oil can contain paraffin even after dewaxing. Paraffin crystallizes at low temperatures and can thus rapidly increase the viscosity of the oil. Pour point depressants do not prevent crystallization but can change the shape of the crystals and reduce the viscosity increase caused by paraffin crystallization. Pour point depressants can include polyalkyl methylacrylates.

[0032] Antiwear additives can include compounds having an alkyl group, zinc, and phosphorus. For example, suitable antiwear additives may be zinc dialkyl-dithiophosphate derivatives that can also function as antioxidants and corrosion inhibitors.

[0033] Antioxidants can include primary antioxidants that may be free radical scavengers to prevent oxidation and sludge formation resulting from oxidation, and secondary antioxidants that can decompose peroxides formed during oxidation to prevent sludge formation. As mentioned above, zinc dialkyl-dithiophosphate can be used as a primary antioxidant. Typical secondary antioxidants include organic sulfur compounds.

[0034] Corrosion inhibitors prevent rusting in the engine. Rust prevention additives block oxygen from coming into contact with iron in the engine block. Zinc dialkyl-dithiophosphate can react with acids and can thus be used as a corrosion inhibitor to prevent the reaction of oxygen with metals in the engine.

[0035] Metal passivators are used to form a film on the metal in the engine to prevent contact of oxygen with the metal. Metal passivators can contain hydrocarbons such as 2,5-dimercapto-1,4-thiadiazole derivatives. 2,5-Dimercapto-1,4-thiadiazole derivatives can also function as sulfur scavengers.

[0036] To prevent the formation of foam in the oil or on the surface of the oil, an anti-foam additive may be added to the oil and may remain in the used oil. For example, dissolved liquid silicone is often used as an anti-foam agent. Organic polymers can also be used as silicone-free anti-foam additives.

[0037] Contaminants can be formed during use or introduced into the engine oil. For example, common external contaminants or contaminants formed by the deterioration of engine gears or materials include water, other automotive fluids (fuel oil and fuel additives, transmission fluid, brake fluid, waste gasoline, etc.), non-automotive lubricating oils or industrial oils (such as hydraulic oil), dust, salt, sludge, soot, carbonaceous particles, lacquer, oxidation products, etc. Contaminants formed from additives or contaminants formed by engine wear can include metals, metal oxides or particles, and polymers. Contaminants can contain zinc, calcium, phosphorus, silicon, etc. In particular, phosphorus and silicon are difficult to remove by distillation and can impair the action of the hydrogenation catalyst. UMO can also contain coolants such as ethylene and propylene glycol.

[0038] Used oil such as UMO can contain about 75 wt% to 80 wt% of lubricating oil molecules, and these lubricating oil molecules can be re-refined and recovered to form high-quality base oil. In some embodiments, the main contaminants removed from UMO are water, sludge, corrosion precursors, and catalyst poisons. Corrosion precursors can contain organic chlorides and sulfides at levels of 10 to 50 ppm in UMO.

[0039] The used oil can be pre-treated or refined to produce refined used oil. In this disclosure, "refined oil" refers to any used oil or crude oil that has undergone one or more refining processes to completely or partially remove impurities such as water, light fuel, or other compounds (including ethylene glycol, particulate matter, metals). Water can be removed by a dehydration process. The refining process can also include distillation such as vacuum distillation. Some impurities or contaminants may still be present in the refined used oil. Different refining processes can be used to remove different impurities and contaminants. Depending on the specific application, it may not be necessary to remove all impurities or contaminants prior to 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 refined used oil.

[0040] Partially refined oils with various impurities / contaminants at various levels (percentages) can be used in various applications without further refining or re-refining or upgrading. For example, in some related industries, partially refined oils can include oils such as vacuum gas oil (VGO), light VGO (LVGO), heavy VGO (HVGO), marine gas oil (MGO), or oils with similar components or properties. However, this disclosure is concerned with further refining and re-refining or upgrading of the refined used oil.

[0041] The refined oil may be a distillate comprising a partial distillate obtained by distilling the used oil. The distillation process may include flash distillation of the used oil. In some embodiments, atmospheric distillation or vacuum distillation may also be included. In the related industry, the term "distillate" may also refer to diesel fuel, fuel oil, kerosene, etc. Typically, the oil distillate has a flash point of less than about 100°F. Typically, the distillate may also have an initial boiling point (IBP) of 400°F and a final boiling point (FBP) of 700°F. A typical partial distillate may have an IBP - FBP range that overlaps with the range of 400 - 700°F. For example, the partial distillate may have an IBP - FBP range of 300 - 500°F or 500 - 800°F.

[0042] VGO and MGO are examples of distillates.

[0043] Some embodiments disclosed herein relate to processes and systems for treating used oil in a pretreatment facility such as a contaminant separation unit (CSU) to separate and remove various contaminants from the used oil to obtain a partially refined oil fraction.

[0044] Removal of such contaminants can reduce or avoid plugging, fouling, and corrosion and improve the overall system performance and efficiency because at least some potential contaminants can cause plugging, fouling, or corrosion in downstream processing facilities.

[0045] In some embodiments, the refined oil is processed in a solvent extraction unit, also referred to as a molecular separation unit (MSU), to separate solvent-soluble compounds from the solvent-insoluble compounds in the feedstock. Depending on the extraction solvent used, the extract in the extract stream may contain low-quality base oil, and the non-extracted fraction of the feedstock (referred to as raffinate or raffinate stream) may contain high-quality base oil. Typically, the extraction solvent and extraction conditions can be selected to separate and remove oxygenates, unsaturates (unsaturated hydrocarbons), and aromatics (aromatic hydrocarbons) from the saturates (saturated hydrocarbons) in the feedstock. The process can also improve the color index of the raffinate stream.

[0046] The extract from the solvent extraction process contains a low-quality base oil fraction and undergoes a continuous-flow liquid-phase hydrogenation process to produce high-quality oil products that may include high-quality base oil, ultra-low sulfur diesel, or naphtha. The hydrogenation process is used to remove aromatics and other unwanted materials and convert unsaturates to saturates. It is desirable to convert as many unsaturates to saturates as possible, provided it is economically and technically viable. Saturates are desirable because they are more stable and less prone to decomposition over time or under harsh conditions such as exposure to heat, moisture, or reactive substances (such as reactive gases).

[0047] The oil products obtained by the processes described herein may contain oils having boiling points between 550°F and 1050°F and oils that may contain C 18 ~C 40 hydrocarbons (i.e., hydrocarbons having 18 to 40 carbon atoms).

[0048] Typically, used base oils and finished lubricating oils can become contaminated by use or handling with oxidation and decomposition products, water, fuel, solvents, antifreeze, other oils, particulate matter, additive products, etc. Use can also cause changes in the molecular structure of the hydrocarbons or chemical additives in the oil. These contaminants or changes can reduce the performance of the used oil, or make the oil unsuitable for use in the intended service, requiring disposal or replacement with new uncontaminated oil. When considered unsuitable for use or service, these contaminated oils are typically referred to as used oils or waste oils. Used oils can be either petroleum or synthetic oils. Examples of used oils include oils used as motor oils for automobiles, cars, trucks, or other transportation vehicles; oils as lubricating oils for engines, turbines, or gears; oils as hydraulic oils, metalworking fluids, insulating fluids, coolant fluids, or process fluids, etc.

[0049] Treatment of used oil in the CSU can include distilling the used oil stream and separating at least a portion of the feedstock having a boiling point of less than about 350°F from the used oil to produce a de-volatized oil fraction and a light oil fraction.

[0050] Treat the de-volatized oil fraction to separate at least a portion of the material having a boiling point above about 350°F to produce a fuel oil fraction and a heavy oil fraction.

[0051] Treat the heavy oil fraction to separate at least a portion of the material having a boiling point from about 650°F to less than 1200°F to produce a partially refined oil fraction and a residue fraction.

[0052] In some embodiments, the light oil fraction is separated from the de-volatized oil fraction by distillation such as at least one of atmospheric distillation or vacuum distillation.

[0053] In some embodiments, the fuel oil fraction is separated from the heavy oil fraction by at least one of atmospheric distillation or vacuum distillation. In some embodiments, the partially refined fraction is separated from the residual oil fraction by vacuum distillation.

[0054] Of course, the CSU may be configured and designed to perform a preliminary separation of useful oil fractions from some unwanted materials and low-quality oils. Unwanted materials that can be removed at this stage can include heavy materials such as asphalt, and some contaminants that can be removed along with the asphalt. To facilitate the removal of specific materials, selected additives may be added to the process stream. Contaminants that can be removed can also include acidic compounds, additives added to motor oil during manufacture, rubber, varnish, dust particles, and the like. Materials that can be removed at this stage can also include light materials such as water, glycol, coolant, antifreeze, and the like. Gases such as light gasoline components can also be removed in the CSU.

[0055] Next, the partially purified oil fraction from the CSU is subjected to solvent extraction in a solvent extraction column or MSU to separate the high-quality base oil fraction from the low-quality base oil fraction in the purified oil.

[0056] The extraction solvent can be selected to mainly extract aromatic substances and polar compounds.

[0057] The extraction solvent may be n-methyl-2-pyrrolidone (NMP). In some embodiments, NMP may be used in combination with one or more other solvents. For example, a mixture of NMP and phenol may be used for solvent extraction. The extraction solvent may also contain a small amount of water.

[0058] In different embodiments, the extraction solvent can 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 - butyrolacetone, water, aqueous salts, low - alkyl - ester of low mono - and dicarbonic acids, dimethylformamide, 2 - pyrrolidone and N - (low alkyl)2 - pyrrolidone, N - methyl - 2 - pyrrolidone, mono or poly protic acids, mineral acids, carboxylic acids, hydroxide bases, carbonate bases, mineral bases, epichlorohydrin, dioxane, morpholine, low - alkyl - and amino(low - alkyl)morpholine, benzonitrile and di - (low - alkyl)sulfoxide and phosphonate.

[0059] The solvent extraction column may be designed to limit entrainment and allow for good separation of the oil and extractant phases.

[0060] In some embodiments, the extract from the MSU may be processed by hydrogenation in a hydrogenation unit, also referred to herein as a molecular treatment unit (MTU) or a hydrotreating unit, to improve the quality of those oils. The hydrogenation treatment may include adding a hydrogen diluent to the stream of extract from the MSU to form a continuous liquid phase diluent and feed mixture. Hydrogen is then added to the diluent and feed mixture to form a continuous liquid phase feedstock, diluent, and hydrogen mixture. The continuous liquid phase feedstock, diluent, and hydrogen mixture is then reacted in the presence of a hydrogenation catalyst to remove selected compounds from the feed mixture, thereby obtaining high-quality base oils, ultra-low sulfur diesel, or naphtha.

[0061] In some embodiments, the continuous flow liquid phase hydrogenation treatment step may be carried out in a hydrogenation reactor at a predetermined temperature. The reactor may be configured to have an upper region gas and a lower region substantially larger, with hydrogen dissolved in the liquid mixture surrounding the hydrogenation catalyst.

[0062] The method further includes subjecting the used oil stream to ozonation, oxidation, acid treatment, and / or magnetic filtration before feeding it to the contaminant separation device, and / or subjecting the partially purified oil fraction to ozonation, oxidation, acid treatment, and / or magnetic filtration before feeding it to the contaminant separation device.

[0063] Ozonation can be carried out using a mixture of about 1.2% ozone in oxygen. Since the interface between the gas and the liquid (oxygen and used oil) is important, a packed column can be used to use ozone more efficiently. Oxidation can be carried out using hydrogen peroxide (50%) and ultraviolet (UV) light.

[0064] Acid treatment may require treatment with an organic acid such as glacial acetic acid, and the ratio of oil to acid is 10:1.

[0065] Magnetic filtration can be carried out by methods known in the art.

[0066] In some embodiments, the used oil stream can be pretreated with chemical additives before entering the contaminant separation device. The chemical additives can include additives selected from butanol, amines, sodium, and hydrogenating agents, or combinations thereof.

[0067] A specific embodiment is illustrated in FIG. 1 showing a schematic diagram of a system 5 for refining and upgrading used oil, including UMO and other waste oils.

[0068] System 5 includes a feedstock container 10, a contaminant separation unit (CSU) 14, a molecular separation unit (MSU) 22, and a molecular treatment unit (MTU) 30. A transport line 12 connects the feedstock container 10 and the CSU 14. An outlet line 16 is provided to discard contaminants and impurities separated from the feedstock in the CSU 14. A transport line 18 connects the outlet of the CSU 14 and the inlet of the MSU 22 to transport the refined base oil from the CSU 14 to the MSU 22. The MSU 22 has an outlet line 24 for discharging the raffinate stream produced in the MSU 22. A transport line 26 connects the outlet of the MSU 22 and the inlet of the MTU 30 to transport the extract stream formed in the MSU 22 to the MTU 30 for further processing. A transport line 28 connects the outlet line 20 of the CSU 14 and the inlet of the MTU 30 to transport the light oil separated from the refined oil in the CSU 14 to the MTU 30 for further processing.

[0069] The CSU 14 is structured and configured to separate and remove physical contaminants (including asphalt) from the base oil component (base oil fraction) in the feedstock. In particular, the outlet line 16 may be used to discard the removed contaminants or impurities, the transport line 18 may be used to discharge the refined base oil fraction in the liquid phase, and the outlet line 20 may be used to discharge the separated oil in the gas phase.

[0070] A specific example of the configuration of the CSU14 is illustrated in FIG. 2 (see Step 1).

[0071] The CSU14 may generally include a packed column, which is also referred to as a packed tower. For example, the packed column may typically be in the form of a cylindrical container filled with a packing material. The feedstock is typically circulated from the top to the bottom, and a purifying agent such as soda ash may be injected into the column from the top of the column into the liquid phase. The soda ash can be injected using a spray nozzle installed at the top of the column.

[0072] In some embodiments, the CSU14 includes a vacuum separation column instead of a thin-film evaporator commonly used for separating contaminants at a crude oil refinery.

[0073] The CSU14 is typically used as part of the pretreatment of the feedstock. The CSU14 may also include a distillation facility for removing water and other impurities or contaminants based on the boiling point or vapor pressure of the materials.

[0074] During operation, the feedstock stored in the container 10 is introduced into the CSU14 through the transport line 12 using, for example, a pump or a suitable conveying device. The flow rate in the transport line 12 can be controlled using a transport pump or a flow rate control valve (not shown).

[0075] The feedstock may include used oil (such as UMO), used industrial oil, or a combination thereof. When explaining and illustrating the operation of the processes and systems shown in the drawings, UMO is often referred to in this specification, but other used oils can also be used as the feedstock or in the feedstock.

[0076] The feedstock may contain various contaminants, including water, light hydrocarbons, solvents, solids, polymers, high molecular weight hydrocarbons, lubricant additives, chemicals, salts, etc.

[0077] At least some of the physical contaminants or impurities are removed from the feedstock in the CSU14.

[0078] Various physical contaminants can be removed from the base oil fraction and the gas fraction. The removed physical contaminants can be separated into a plurality of discharge streams through a plurality of outlet lines. The removed physical contaminants may include low molecular weight materials such as water, glycol, asphalt, etc. The removed contaminants may also include impurities in the gas phase.

[0079] Some of the sulfur in the feedstock can also be removed in CSU14. Sulfur can react with chemicals to form precipitates. The precipitates can then be removed together with other separated contaminants such as asphalt.

[0080] Separation in the CSU can be achieved using several processes or combinations of processes, including various forms of extraction, distillation, filtration, centrifugation, absorption, adsorption, etc., known to those skilled in the art. Typically, the separation is achieved based on some differences in the physical or chemical properties of the materials to be separated.

[0081] Separation in CSU14 may be achieved using various conventional systems and techniques.

[0082] Therefore, CSU14 can be used to purify the feedstock and produce refined oil. The refined oil may include refined base oil. For example, if the feedstock contains UMO, the refined oil discharge fraction at line 18 may contain refined base oil. The refined oil discharged through line 18 does not need to be completely refined. The refined oil fraction of line 18 contains a lower ratio of impurities or contaminants compared to the feedstock.

[0083] The base oil fraction extracted through outlet line 18 may contain saturated and unsaturated hydrocarbons suitable for use as a base oil or for further processing to produce a base oil. Suitable hydrocarbon molecules typically have 18 to 40 carbon atoms and a boiling temperature of about 500°F to about 1200°F at 1 atm.

[0084] The base oil fraction extracted from line 18 is introduced into MSU22 and, through a stirred liquid-liquid solvent extraction process, an extract stream containing low-quality base oil is produced. This low-quality base oil is extracted through line 26 and transported to MTU30 for further processing to form a raffinate stream containing high-quality base oil, which is discharged through outlet line 24.

[0085] The raffinate stream can meet the Group II or Group III base oil standards and contains high-quality base oil that can be used as Group II or III base oil. Some of these high-quality base oils are commercially available without further processing or treatment, but may also be further processed, such as by including desired additives.

[0086] The extract stream from MSU22 contains low-quality oil that may or may not meet the Group I base oil standards and undergoes a continuous-flow liquid-phase hydrogenation process in MTU30 to increase the saturation level and viscosity index and reduce the sulfur level. The treatment in MTU30 can also remove aromatic substances and various elemental contaminants from the raffinate stream. For example, the extract stream may contain elemental sulfur bonded to hydrocarbons. Such sulfur-containing compounds react with hydrogen to form H 2 S gas and saturated hydrocarbons, thereby removing sulfur from the hydrocarbons. H 2 S gas can be separated from the liquid stream containing increased saturates. Other possible contaminants that may be present in the raffinate stream and can be removed in MTU30 include polymers, metals, phosphorus, silicon, etc. The process in MTU produces an oil product with improved quality in terms of saturation level, sulfur level, and viscosity index, and possibly other aspects. The product from MTU30 may include high-quality base oil fractions, ultra-low sulfur diesel, or naphtha, or combinations thereof. The high-quality base oil can meet the Group II or III standards described in API 1509.

[0087] In some embodiments, at least one fraction of the light oil obtained in CSU14 can also be introduced into MTU30 through line 20, either separately or together with the extract stream from MSU22 passing through line 28.

[0088] In MSU22, the refined oil stream is separated into at least two streams by solvent extraction. The extract stream typically contains a significant amount of oxygenated substances, aromatics (aromatic hydrocarbons), unsaturated substances (unsaturated hydrocarbons), and may also contain low levels of saturated substances. The extract can contain polar compounds, aromatic hydrocarbons, olefins, unsaturated substances, heteroatoms, etc. The extract stream initially also contains most of the extraction solvent, which can subsequently be separated and removed as further discussed below. Since the extract has low levels of saturated substances and a low viscosity index (VI), it is considered to contain low-quality base oil.

[0089] The raffinate stream separated from the extract stream can contain higher-quality base oil because it can have higher levels of saturated substances, lower levels of sulfur, and a relatively higher VI. The raffinate stream can also have reduced levels of aromatics. The saturated substances in the raffinate stream are typically paraffinic and non-aromatic.

[0090] The raffinate stream having higher-quality base oil can be discharged through outlet line 24 to produce a base oil product. The base oil product may contain at least 90 wt% saturated substances and less than 0.03 wt% sulfur, and can have a VI of at least 120. In some cases, the base oil product extracted from outlet line 24 may contain at least 95 wt% saturated substances.

[0091] Depending on the nature of the feedstock and the processes carried out in CSU14 and MSU22, the extract stream discharged at line 26 typically contains high concentrations of unwanted materials (such as sulfur, oxygen, nitrogen, olefins, aromatics, etc.).

[0092] Using various processes or combinations thereof, separation or removal of these unwanted materials from the saturated substances in the extraction stream may be achieved, and the unsaturated substances may be saturated by hydrogenation. For example, MSU22 or MTU30 or both may include equipment or sub-units for performing various forms of extraction, filtration, ultrafiltration, absorption, adsorption, hydrogenation, etc., and known techniques such as catalysts and molecular sieves may be used to assist or enhance the treatment and performance.

[0093] In MTU30, the extract from MSU22 is treated under continuous flow liquid phase hydrogenation conditions to increase the saturation level and VI, and optionally reduce the sulfur level and the level of aromatics. The oil products produced in MTU30 may include base oils containing at least 90 wt% saturated substances and less than 0.03 wt% sulfur and having a VI of at least 80. In some embodiments, the oil products may contain at least 95 wt% saturated substances and the VI may be 120 or more. The oil products may also include ultra-low sulfur diesel and naphtha. The oil products may be extracted through the outlet line 32.

[0094] The oil products extracted from line 32 may be of a quality sufficient to meet the Group II or III standards as described in API 1509.

[0095] Figure 2 illustrates further details of the system 5 according to a particular embodiment.

[0096] As seen in Figure 2, CSU14 may be implemented in zone 40 for the processing and treatment of the first stage (stage 1), MSU22 may be implemented in zone 50 for the processing and treatment of the second stage (stage 2), and MTU30 may be implemented in zone 60 for the processing and treatment of the third stage (stage 3).

[0097] In stage 1, CSU14 in zone 40 includes a distillation system for separating the base oil fraction in the feedstock introduced through the inlet line 42 from other components.

[0098] The system of zone 40 includes an inlet line 42, heaters 44, 84, 104, 128, transport lines 46, 54, 56, 76, 78, 82, 83, 96, 98, 102, 106, 108, 118, 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.

[0099] The flash distillation vessel 52 includes a top 53 and a bottom 57. Line 54 is the distillate outlet line of the flash distillation vessel 52 for discharging the distilled product stream produced therein. Line 56 is the bottom outlet line for transporting the bottoms formed in the flash distillation vessel 52 to the flash distillation vessel 70.

[0100] The flash distillation vessel 70 includes a top 72 and a bottom 74. Line 76 is the distillate outlet line of the flash distillation vessel 70 for discharging the distilled product stream produced therein. Line 78 is the bottom outlet line for transporting the bottoms formed in the flash distillation vessel 70 through the pump 80, line 82 and heater 84, and through line 86 to the flash distillation vessel 90, or to the recycling line 83 for returning to the flash distillation vessel 70. The pump 80 propels the flow rate in the transport lines 78, 82, 83, and 86. The heater 84 heats the fluid transported through line 82.

[0101] The vacuum distillation vessel 90 includes a top 92 and a bottom 94. Line 96 is the distillate outlet line of the vacuum distillation vessel 90 for discharging the distilled product stream produced therein. Line 98 is the bottom outlet line for transporting the bottoms formed in the vacuum distillation vessel 90 through the pump 100, line 102 and heater 104, and through line 106 to the vacuum distillation vessel 112, or to the recycling line 106 for returning to the vacuum distillation vessel 90. The pump 100 propels the flow rate in the transport lines 98, 102, 106, and 108. The heater 104 heats the fluid transported through line 102.

[0102] The vacuum distillation vessel 112 includes a top 114 and a bottom 116. Line 118 is a distillate outlet line of the vacuum distillation vessel 112 for discharging the distillation stream produced in the vacuum distillation vessel 112. Line 120 is a bottom outlet line for transporting the bottom stream formed in the vacuum distillation vessel 112 through pump 122 and line 124 to obtain an oil product or to perform further processing, or for recycling the bottom stream (or a portion thereof) back to the vacuum distillation vessel 112 through line 126, heater 128, and line 106. Pump 122 propels the flow rates in transport lines 120, 124, and 126. Heater 128 heats the fluid transported through line 126.

[0103] During operation, the feedstock is introduced into the first flash distillation vessel 52 through lines 42, 46, and heater 44 and undergoes a distillation process. The distillation temperature in vessel 52 is controlled and adjusted to allow the boiling of water and low-boiling hydrocarbons. The typical distillation temperature is determined by the used oil supplied and the selected operating pressure and may range from about 190°F to about 210°F. The distillation stream has a boiling point of up to about 350°F at 1 atm, is produced and collected at the top 53 of the flash distillation vessel 52. Naturally, such a distillate having such a boiling point contains light oil. The distillate is recovered via line 54 and can be used as fuel oil or the like. The bottom stream formed and collected at the bottom 57 may contain the liquefied oil fraction in the feedstock, is discharged through the bottom outlet line 56, and is transported to the in-situ flash distillation vessel 70.

[0104] The first distillation process separates and removes light hydrocarbons and water from the bottom stream of vessel 52.

[0105] The underflow of vessel 52 undergoes further distillation in vessel 70. The distillation temperature in vessel 70 may range from about 280°F to about 295°F. The distillate stream produced and collected at the top 72 of vessel 70 is discharged through outlet line 76. The underflow formed at the bottom 74 of vessel 70 is discharged through outlet line 78 to recover a portion of the liquid layer maintained at the lower part of vessel 70 at the liquid level indicated by 88.

[0106] The distillate stream recovered from line 76 generally has a boiling point in the range of about 350°F to about 500°F. Thus, the distillate stream of vessel 70 can be used as fuel oil.

[0107] The underflow formed in vessel 70 contains heavy oil. A fraction of the underflow of vessel 70 may be recycled by passing it through line 78, pump 80, supply inlet line 82, heater 84, and line 83. Another fraction of the heated underflow in line 82 may be transported through line 86 to a third vacuum distillation vessel 90.

[0108] The heated underflow of vessel 70 is further distilled in vessel 90. The distillation temperature in vessel 90 may range from about 280°F to about 320°F. The distillate stream formed and collected at the top 92 of vessel 90 also contains oil that can be used as fuel oil. The distillate stream has a boiling point in the range of about 500°F to about 650°F.

[0109] In this vacuum distillation process, non-volatile fractions including fuel fractions, light oil, and heavy residual oil are separated.

[0110] The underflow formed and collected at the bottom 94 of vessel 90 contains heavy oil. A portion of the underflow passes through lines 98, 102, 108 and pump 100, is heated by heater 104, and then recycled back to vessel 90. A portion of the heated underflow passes through line 106 as feedstock to a fourth vacuum distillation vessel 112. The liquid volume at liquid level 110 is maintained at the lower part of vessel 90.

[0111] The heated bottoms returned for vessels 70 and 90 are used to maintain the temperature in the liquid layer at the bottoms 74 or 94 of vessels 70 and 90 respectively.

[0112] The feed materials to vessels 70 and 90 are heated to a sufficiently high temperature necessary to achieve the desired separation of the distillate by bringing them into direct contact with the liquid layer at the bottoms of vessels 70 and 90.

[0113] The bottoms fraction fed from vessel 90 to vessel 112 undergoes further distillation in vessel 112 at a high temperature of up to about 560°F. Vessel 112 is configured and operated to produce a distillate stream having a boiling point of about 650°F to about 1200°F at the top 114. The distillate stream is discharged through the distillate outlet line 118.

[0114] The liquid level 130 is also maintained at the bottom 116 in vessel 112. A portion of the bottoms formed at the bottom 116 is heated and recycled back to vessel 112 through line 120, pump 122, heater 128, and line 106. The returned heated bottoms helps to maintain the desired feed temperature to vessel 112. Another portion is discharged through line 124 and can be used as a product or can undergo further processing. For example, the discharge from line 124 may be transported to a storage container (not shown) for storage.

[0115] Depending on the original feedstock, the bottoms recovered through line 124 typically contains asphalt, polymers, high-boiling hydrocarbons, salts, solids, and other high-boiling materials having a boiling point above 1200°F.

[0116] In some embodiments, vessel 112 may be a vacuum distillation vessel, for example, to prevent the decomposition of any base oil fraction in the feed material to vessel 112. Steam or gas stripping can also be used in vessel 112 to enhance the distillation.

[0117] The distillate stream recovered from vessel 112 at line 118 contains refined used oil. The refined used oil may be partially refined as described above. The refined used oil is transported to MSU22 in zone 50 for further processing and treatment in stage 2, including agitated solvent extraction.

[0118] MSU22 in zone 50 includes heat exchanger 132, agitated countercurrent liquid-liquid extraction column 140, solvent system 148, vessel 152, and solvent separation vessel 154, as well as transport lines 134, 150, 155, 156, 157, 164, 166, 172 connecting these to each other. For simplicity, agitated countercurrent liquid-liquid extraction column 140 is also referred to as solvent extraction column 140.

[0119] Heat exchanger 132 is configured and arranged to heat the distillate stream from outlet 118 of distillation vessel 112 before the distillate is introduced into solvent extraction column 140 through line 134.

[0120] Solvent extraction column 140 has a bottom 142, a top 144, a contact section 146 between the bottom 142 and the top 144, an inlet connected to transport line 150 for introducing the extraction solvent into solvent extraction column 140, a top outlet connected to transport line 157, and a bottom outlet connected to line 155.

[0121] Solvent extraction column 140 also includes a variable-speed agitator (not shown one by one in Figure 2 but can be referenced in Figure 3) configured and operative to agitate the refined oil and extraction solvent flowing through solvent extraction column 140 at a variable agitation speed. The agitation speed can be controlled independent of the flow rate of the fluid in solvent extraction column 140. The agitator may be a rotary agitator, a reciprocal agitator, a pulsed agitator, etc.

[0122] A specific example of the solvent extraction column 140 is a countercurrent liquid extraction device known as a Scheibel column in the art. A general description of the Scheibel column is described in US2493265 (by Scheibel, titled "Extraction Apparatus", published in 1950). A suitable Scheibel column may be a vertical column in which the refined oil and the extraction solvent are contacted countercurrently.

[0123] Figure 3 schematically shows the basic structure of a typical Scheibel extraction column 300 that can be used as column 140. The extraction column 300 includes a vertical container 302, a lower inlet 304 for introducing a first liquid phase into the column 300, an upper inlet 306 for introducing a second liquid phase into the column 300, an upper outlet 308 for discharging the first liquid phase, a lower outlet 310 for discharging the second liquid phase, and two inlet / outlet portions 312 and 314 for interface control. The first liquid phase is the light phase and the second liquid phase is the heavy phase. For example, when the extraction solvent is NMP and the feedstock contains a base oil lighter than NMP, the NMP solvent is the heavy phase and is introduced into the column through the upper inlet 304, and the feedstock is introduced into the column through the lower inlet 302.

[0124] The extraction column 300 has an inner chamber and a number of horizontally installed baffles 316 and 318 that are configured and arranged to improve the countercurrent mixing and contact within the chamber as the two liquid phases flow through the chamber in opposite directions. Baffle 316 is an external baffle and baffle 318 is an internal baffle. Of course, baffles 316 and 318 are arranged to improve the mixing efficiency.

[0125] The stirrer 320 is installed to stir the liquid phase when it passes through the extraction column 300. The stirrer 320 includes a rotating shaft 322 that extends vertically through the center of the column chamber, and a speed variator 324 for activating and driving the shaft 322. A number of turbine impellers 326 are attached to the shaft 322 and are arranged to avoid contact with the internal baffle 318. When the shaft 322 rotates by the driver 324, the impeller 326 stirs the liquid phase in the extraction column, further improving mixing and contact. Therefore, efficient mixing of the two liquid phases and efficient solvent extraction can still be achieved even when the liquid phase flows at a relatively high speed. The stirring speed or rotational speed of the shaft 322 can be controlled and adjusted according to the flow rate and other operating parameters or conditions.

[0126] The solvent system 148 is configured to process and store the extraction solvent. The extraction solvent may be NMP. The solvent system 148 is connected to the solvent extraction column 140 by a transport line 150 to supply the extraction solvent stored in the solvent system 148 to the solvent extraction vessel 140. The solvent system 148 has a first inlet connected to line 164 to receive the solvent recycled from container 152, and a second inlet connected to line 166 to receive the solvent returned from the solvent separation container 154.

[0127] The container 152 has a top 158, a bottom 160, an inlet connected to line 157, a top outlet connected to line 164, and a bottom outlet connected to line 156.

[0128] The solvent separation container 154 has a top 168, a bottom 170, an inlet connected to line 155 to receive the bottom fraction from the solvent extraction container 140, a top outlet connected to line 166 to return the separated extraction solvent to the solvent system 148, and a bottom outlet connected to line 172 to transport the extracted material stream separated and removed in the solvent separation container 140 to the hydrogenation device in zone 60 for hydrogenation in the next stage, stage 3.

[0129] During operation, the distillation stream in line 118 passes through heat exchanger 132 and line 134 and enters solvent extraction column 140 as feedstock for the solvent extraction process. The feedstock includes the refined oil described above. The feedstock is driven to flow upward and forms an upward flow in contact section 146. The extraction solvent supplied from solvent system 148 is introduced into the top 144 of the solvent extraction column through line 150, driven to flow downward, and forms a downward flow in contact section 146. Thus, the extraction solvent and the feedstock come into contact as countercurrent. The extraction temperature in contact section 146 is maintained at a temperature lower than the critical temperature at which the oil components in the extraction solvent and the feedstock become completely miscible. For example, when NMP is used with optionally low concentrations of water (e.g., up to 1 vol%), the extraction temperature may range from about 100°F to about 150°F. The volume ratio of the extraction solvent to the feedstock may be about 1 to about 4, depending on the quality and properties of the feedstock and the selected flow rates. Compounds in the feedstock that are soluble in the extraction solvent at the extraction temperature dissolve and disperse in the extraction solvent and are thus separated from compounds in the feedstock that have low solubility or are insoluble in the extraction solvent at the extraction temperature. The dissolved compounds are "extracted" by the solvent and are thus the extract. The undissolved and unextracted compounds, generally referred to as raffinate, are discharged as a raffinate stream through line 157 to solvent separation vessel 152. The raffinate stream also contains a small amount of the extraction solvent (e.g., less than 10 vol%). The extraction stream contains the extraction solvent and the extracted compounds (extract), descends, and is discharged through line 155 to solvent separation vessel 154.

[0130] The ratio of the flow rate of the extraction solvent to the flow rate of the feedstock may be adjusted according to the quality of the oil in the feedstock. For example, the flow rates may be adjusted such that the ratio of the solvent to the feedstock in contact section 146 can be about 1 to about 4. In some embodiments, the ratio of the solvent to the feedstock may be about 3 or about 2.5.

[0131] Advantageously, the variable speed stirrer can control and adjust the stirring speed without affecting the flow rate. The stirring speed can be selected and controlled based on the quality and properties of the feedstock and the selected flow rates.

[0132] The contact part 146 is heated so that the desired extract has a solubility high enough for it to dissolve and disperse in the extract stream containing the extraction solvent. The temperature is not too high, and thus the selected hydrocarbon does not dissolve in the extraction solvent and remains in the raffinate stream.

[0133] The temperature in the solvent extraction column can be selected and controlled according to known techniques or knowledge, based on the quality and properties of the feedstock. Even when the flow rate is slow, the feedstock and the extraction solvent can be sufficiently and rapidly mixed by a stirrer for contact.

[0134] Therefore, the variable-speed stirrer brings about improved efficiency and enables convenient control and adjustment to accommodate possible variations in the feedstock.

[0135] The raffinate stream may contain high-quality base oil. The raffinate stream is transported from the top of the solvent extraction column 140 through line 157 to the separation vessel 152. The high-quality base oil is separated from the extraction solvent in the separation vessel 152, for example, by heating to a temperature higher than the boiling point of the solvent and lower than the boiling point of the base oil. The separated solvent returns to the solvent system 148 through line 164 or is returned for recycling. The separated base oil is discharged through line 156 and can be used as a high-quality base oil product meeting the Group II or III base oil standards specified in API 1509 or can be further processed to produce such a high-quality base oil product. In some embodiments, the base oil product can meet the Group I base oil standards. Line 156 can send the oil product directly or indirectly to the outlet line 24.

[0136] Some of the extraction solvent is recovered through line 164 and returned to the solvent treatment and storage system 148.

[0137] The extract stream containing the extraction solvent and the dissolved or dispersed oil is withdrawn at the bottom of the solvent extraction column 140 and introduced into the solvent separation vessel 154 through line 155. The compounds dissolved or dispersed in the solvent typically include low-quality base oil.

[0138] The extraction solvent is separated from the low-quality base oil in the solvent separation vessel 154, for example, by heating and distillation.

[0139] The separated extraction solvent is recovered from the top 168 of the solvent separation vessel 154 and returned to the solvent system 148 through line 166.

[0140] In the solvent system 148, using techniques known to those skilled in the art, the solvent recycled from both lines 164 and 166 can be treated to remove water and low-boiling contaminants, neutralize its acidity, or otherwise improve the quality of the recycled solvent. The treated solvent is stored in the solvent system 148 for repeated use.

[0141] The low-quality base oil separated in the vessel 154 moves via line 172 to the third stage (stage 3) and undergoes further treatment with MTU 30 in zone 60.

[0142] In stage 2, depending on the quality and properties of the feedstock, the recycle ratio can be adjusted to optimize the solvent extraction process.

[0143] The solvent extraction process can also be conveniently adjusted or modified with the aid of a variable-speed agitator in response to changes in stage 1 or stage 3 or the quality and properties of the feedstock. Thus, the entire system 5 is more adaptable than a batch system or a system that uses continuous solvent extraction but without an adjustable agitation or stirring speed. Therefore, the system 5 is more robust.

[0144] MTU 30 in zone 60 is a continuous-flow liquid-phase hydrogenation treatment unit.

[0145] In previous or conventional systems for refining used oil, hydrogenation is typically carried out in the gas phase. Currently, by using the liquid phase hydrogenation process in combination with other equipment in Zone 40 and Zone 50, it has been recognized that the systems or processes described herein provide better temperature control, maintain continuous operation for a long period of time, and can be more easily adjusted or modified without interrupting the operation or process flow. Further, the lifespan of the hydrogenation catalyst used in the hydrogenation process can be extended as further discussed below. In particular, the introduction and discharge flow rates in the solvent extraction stage may be variable and can be reduced to low flow rates in the embodiments described herein. Thus, MTU30 and the liquid phase hydrogenation process are designed to operate effectively and efficiently even at low throughput or feedstock flow rates.

[0146] MTU30 in Zone 60 includes a heat exchanger 174 located on a transport line 172 for heating the extraction stream from the solvent separation vessel 154, an inlet 176 for a diluent on the transport line 172, a guard bed 178 downstream of the inlet 176 for the diluent, a mixer 187, an inlet 188 for hydrogen injection located downstream of the inlet 176 for the diluent and upstream of the mixer 187, a hydrogenation reactor 190, a stripper / fractionator 202, and transport lines 186, 188, 200, 201 for interconnecting these as shown in FIG. 2.

[0147] The guard bed 178 has a top 180, a bottom 182, and a contact zone 184. In some embodiments, the contact zone 184 may contain used catalyst or activated clay, etc., which are selected to pass through the guard bed 178 and remove contaminants such as silicon and phosphorus from the liquid (the contaminants can have an adverse effect on the hydrogenation catalyst in the hydrogenation reactor 190). Thus, the guard bed 178 protects the hydrogenation reactor 190.

[0148] The mixer 187 is configured to stir the internal liquid mixture and thoroughly mix the hydrogen injected through the hydrogen inlet 188 with the refined liquid mixture before the liquid mixture is introduced into the hydrogenation reactor 190.

[0149] The hydrogenation reactor 190 includes three stacked or superimposed parts. The first part has an upper zone 191, a catalyst bed 192, and a lower zone 193. Similarly, the second part also has an upper zone 194, a catalyst bed 195, and a lower zone 196, and the third part has an upper zone 197, a catalyst bed 198, and a lower zone 199.

[0150] The hydrogenation catalyst is produced in each of the catalyst beds 192, 195, 198. The hydrogenation catalyst may include any catalyst suitable for the hydrogenation process and can be obtained from commercial sources or chemical manufacturers.

[0151] The hydrogenation catalyst may be an inert substance including precious metals such as palladium, gold, nickel, etc. The catalyst promotes the reaction of hydrogen with other molecules, such as unsaturated hydrocarbons, to form saturated substances, or promotes the reaction with sulfur to form H 2 S.

[0152] The stripper / fractionator 202 has outlet lines 204, 206, 208.

[0153] During operation, the extract stream is heated by the heat exchanger 174 before being introduced into the guard bed 178 through line 172.

[0154] Furthermore, a diluent that can increase the solubility of hydrogen in the extract stream is added to the extract stream in line 172 at the diluent inlet 176. The diluent may include a suitable solvent capable of dissolving hydrogen. The diluent is added continuously so that the extract stream introduced into the guard bed 178 has a stable concentration of the diluent. In some embodiments, the diluent can be taken from the outlet of the lower zone 199 of the third part of the reactor 190.

[0155] The diluent and the extract extracted in the solvent extraction column 140 form a liquid mixture, and the hydrogen in the liquid mixture is more soluble than the hydrogen in the extract stream.

[0156] The liquid mixture is introduced into the guard bed 178. The guard bed 178 removes the target contaminants present in the extract from the solvent extraction column 140, which otherwise would impair the action of the hydrogenation catalyst in the hydrogenation reactor 190 and shorten the life of the hydrogenation catalyst.

[0157] The effluent from the guard bed 178 is a purified liquid mixture containing a diluent and low-quality oil. The purified liquid mixture is transported from the guard bed 178 to the mixer 187 through the transport line 186 or by a mixing insert in the injection pipe (not shown) of the reactor 190.

[0158] Hydrogen gas is continuously added to the purified liquid mixture through the hydrogen inlet 188. The hydrogen may be added under a constant pressure, and thus the amount of hydrogen added is stable over time.

[0159] Since the liquid mixture contains a diluent, the added hydrogen can dissolve more rapidly in the liquid mixture, and the liquid mixture can contain a high concentration of hydrogen. As a result, when the mixture is introduced into the hydrogenation reactor 190, the added hydrogen can be present in the liquid phase in the largest amount.

[0160] The mixer 187 discharges a continuous flow of the liquid mixture containing the purified extract, the diluent, and hydrogen in the liquid phase. The liquid mixture flow is introduced into the hydrogenation reactor 190 and undergoes a hydrogenation treatment.

[0161] Compared with a conventional gas-phase trickle-bed hydrogenation treatment reactor in which the hydrogenation reaction rate is limited by the mass transfer of hydrogen from the gas phase / vapor phase into the liquid phase in the reactor, the embodiment described herein and illustrated in FIG. 2 can be operated in a manner that is kinetically limited because the hydrogen is already in the liquid phase when introduced into the reactor 190. Further, the hydrogenation catalyst in the reactor may always be completely wet.

[0162] In addition to, or alternatively to, adding hydrogen at the hydrogen inlet 188, hydrogen may be added at one or more other points along the transport line 186. In some embodiments, additional hydrogen may also be added at various points along the length of the hydrogenation reactor 190 through a mixing insert (not shown) provided in a nozzle (not shown) connecting the lower zone 193 of the first section and the upper zone 194 of the second section, and the lower zone 196 of the second section and the upper zone 197 of the third section.

[0163] However, it has been found that the addition of hydrogen to the liquid mixture and the addition of a diluent prior to the addition of hydrogen upstream of the mixer 187 allow more hydrogen to be present in the liquid phase when the mixture is introduced into the reaction zone in the hydrogenation reactor 190, promoting more efficient operation. Also, by increasing the solubility of hydrogen, it is possible to adjust the flow rate of the liquid feedstock over a wide range without significantly adversely affecting the hydrogenation performance. In particular, continuous flow liquid phase hydrogenation can proceed continuously over a long period of time at a relatively high yield to a high quality base oil product that meets the specifications of Group II or even Group III base oils as defined by API 1509. In some embodiments, the oil product from MTU 30 can meet the specifications of Group III base oils.

[0164] The reaction zone in the hydrogenation reactor 190 may be pressurized to a typical pressure of, for example, 800 psi to 1200 psi and heated to a suitable elevated temperature. The hydrogenation catalyst is selected to promote certain reactions over others, such that the reactions in the hydrogenation reactor 190 preferentially and selectively become those that require molecules with low lubricity values or properties such as unsaturated hydrocarbons or unsaturated substances.

[0165] In the hydrogenation reactor 190, unsaturated hydrocarbons, olefins, elemental contaminants (such as sulfur, nitrogen, oxygen, heteroatoms, etc.) present in the feed stream are hydrogenated. Some of the reaction products are gases and are discharged through the outlets of the upper zones 191, 194, and 197 of each catalyst section. As a result, the oil product extracted from the hydrogenation reactor through line 200 has a high level of saturates, a low level of contaminants (including sulfur), and a low level of aromatics, and has a high viscosity index.

[0166] The upgraded oil product may be further processed before being provided to the customer. For example, the oil product can be transported to a stripper / splitter 202 for further processing.

[0167] In the splitter 202, the saturated hydrocarbons are separated into various fractions that may include one or more of naphtha, diesel oil, and base oil. The various fractions can be discharged through various outlets 204, 206, 208.

[0168] The oil product discharged from MTU30 may have a high concentration of saturated hydrocarbons and volatile compounds of hydrogen. Thus, the produced oil product may contain at least 90 wt% saturates and less than 0.03% sulfur, and may contain an upgraded oil having a viscosity index of at least 80. The saturation level in the oil product may be over 95 wt%. The VI of the oil product may be between 80 and 120, or may be over 120.

[0169] The oil product may be suitable for use as a base oil under Group II or III of API 1509.

[0170] As shown in FIG. 2, a portion of the effluent from reactor 190 may be recycled back to reactor 190 through line 201 and inlet 176. The recycled stream can supply at least a portion of the required hydrogen to reactor 190 and can also function as a heat sink, thus further reducing temperature fluctuations in reactor 190. Accordingly, the processing process in reactor 190 can be more isothermal. Flow control devices (not shown for simplicity and clarity), such as valves, flow meters, or pumps, can be installed in lines 200 and 201 to control and adjust the flow rate in these lines as would be understood by one of ordinary skill in the art. A typical recycle ratio of the oil product to the recycled feedstock may be 3:1. Recycling in this manner is also beneficial when the feedstock entering from MSU22 is temporarily interrupted, because MTU30 can continue to operate using the recycled feedstock at a relatively low feed rate with a low risk of coking and associated plugging in MTU30. A pump (not shown) may be used to recycle the recycle stream from reactor 190 to inlet 176.

[0171] Also advantageously, the recycle stream is an inert hydrogen carrier.

[0172] In some embodiments, make-up hydrogen may be added to the liquid mixture containing the recycle stream, for example, by supplying make-up hydrogen into the system through hydrogen inlet 188. A gas compressor (not shown) may be used to compress the added hydrogen gas.

[0173] As described above, in MTU30, hydrogen is mixed and flowed into the extract stream in the presence of a diluent having a relatively high solubility for hydrogen under a constant pressure. As a result, when the mixture is introduced into hydrogenation reactor 190, hydrogen is present in the liquid phase.

[0174] In some embodiments, excess hydrogen may be added and mixed with a liquid mixture of the extract stream and the diluent, and thus the resulting liquid mixture contains the maximum amount or concentration of hydrogen in the liquid phase and is considered to increase the reaction performance. When the added hydrogen exceeds the maximum amount soluble in a given liquid mixture, a portion of the added hydrogen may remain in the gas phase.

[0175] The type and amount of diluent added, as well as the hydrogenation reaction conditions, can be selected such that sufficient hydrogen is supplied into the liquid phase to promote the hydrogenation reaction or maximize / optimize the reaction performance.

[0176] The diluent may be a solvent and may include propane, butane, or pentane, or combinations thereof.

[0177] The diluent may also be or may include light hydrocarbons, light distillates, naphtha, diesel, VGO, hydrotreated feedstock, recycled hydrocracking products, isomerization products, recycled demetallized products, and the like.

[0178] Advantageously, in the embodiments disclosed herein, more hydrogen is supplied into the liquid phase, so the reaction rate can be increased, the feed flow rate also consequently increases, and operation can be carried out at a very high flow rate.

[0179] Many of the hydrogenation reactions that can occur in reactor 190 are exothermic reactions, and thus, depending on the reaction rate, catalyst conditions, and hydrogen utilization rate, the temperature in the reactor can potentially drift or fluctuate.

[0180] In the above embodiment, when the flow rate of the fluid is high, the temperature in the hydrogenation reactor 190 can be made more stable. The reason is that the temperature is mainly determined by the temperature of the incoming liquid mixture, and any temperature fluctuations caused by the heat generated by the hydrogenation reaction are relatively small. For example, the temperature fluctuations in the embodiments described herein can be controlled within about 5°F. The hydrogenation process can generally be considered isothermal.

[0181] To further offset the influence of any heating or to better control the temperature within the system, an air cooler (not shown) may be installed in the MTU 30.

[0182] Therefore, the continuous flow liquid phase hydrogenation reactor is more advantageous in the system 5 compared to, for example, the trickle bed reactor that has been conventionally used for upgrading used oil.

[0183] Also, it is expected that the MTU described herein can enable operation control with relaxed severity compared to a system for upgrading conventional base oils.

[0184] In some cases, it may be desirable to chemically treat the used oil feedstock with a base or alkaline substance such as sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium hydroxide. Such treatment can be carried out in the heater 44.

[0185] Such treatment can condition, stabilize, or otherwise neutralize the used oil, reduce the risk of fouling within the system, facilitate the separation of the used oil stream into its components, or enhance the quality of all non-base oil by-products.

[0186] In some cases, it may be desirable to add an alkali or base in the feed stream or recycle stream to one or more distillation vessels or directly into the vessel.

[0187] In the above embodiment, four distillation vessels are used to separate the base oil fraction from other components in the used oil. However, in different embodiments, fewer distillation vessels such as two or three, or more distillation vessels such as eight may be used in the CSU to purify the oil feedstock.

[0188] In the above embodiment, the distillation vessel may be a flash vessel. The purification apparatus may include any apparatus or system capable of purifying the oil feedstock, and may include a single-stage separation / purification apparatus, such as an evaporator, a thin-film or wiped-film evaporator, a column, a vessel, a tank, a pipe, etc.

[0189] In the above embodiment, steam or gas can be added to the distillation vessels 52, 70, 90 and 112 to assist in stripping the heavy distillate from the used oil, thereby enhancing the separation / purification.

[0190] Steam stripping is a technique known to those skilled in the art to enhance the distillation process and can be utilized in the system 5.

[0191] In vessel 52, there is no need to heat the recycled bottoms because it is possible to heat the incoming feed stream to the desired temperature with heater 44 without the risk of fouling. Vessel 52 can be operated in the same manner as vessel 70 by heating and returning a portion of the bottoms in line 56 back to vessel 52 to maintain the bottom layer in vessel 52.

[0192] In some cases, it may be desirable to combine the stream recovered through line 96 (i.e., light oil), which typically has a boiling point in the range of about 500°F to about 650°F, with the stream in line 172 for hydrotreating, because this stream may be suitable for use as a base oil. It is not necessary to use this stream to replenish the stream in line 172, but it is an optional option as needed.

[0193] The boiling point range of the material recovered through line 96 can be modified as needed to produce a material with a slightly higher initial boiling point. The stream in line 96 can also be useful as a base oil.

[0194] In the application example in the above-described embodiment of step 2, the extraction solvent needs to have a specific gravity greater than that of the base oil in the feedstock, and thus, a countercurrent flow can be formed in the direction described and illustrated in FIG. 2.

[0195] In different embodiments, the extraction solvent has a specific gravity smaller than that of the base oil to be extracted, and the process and system can be modified to reverse the flow directions of the solvent and the feedstock. That is, the solvent is introduced into the bottom of the solvent extraction vessel, and the feedstock is introduced into the top of the solvent extraction vessel.

[0196] Containers 152 and 154 can still be configured and operated to remove the solvent from the raffinate and the extract, respectively, in a similar manner.

[0197] FIG. 2 shows one guard bed 178 and one hydrogenation reactor 190, but in different embodiments, two or more guard beds arranged in series or parallel can be used before the reactor 190. The parallel guard beds are considered to be operated one by one so that either container can be regenerated or swept and refilled without interrupting the flow to the reactor 190.

[0198] Similarly, a plurality of hydrogenation reactors can be operated in series or parallel to enhance the operation.

[0199] In the above embodiments, it may be desirable to incorporate a hydrogen recovery system for recovering hydrogen from the product stream 200. The hydrogen recovery system could conceivably purify and recover the hydrogen in this stream and recycle it back for use through the hydrogen inlet 188.

[0200] Also, it may be desirable to remove non-base oil light contaminants from the base oil using steam or gas stripping in the vessel 202. The base oil in line 206 could also be further processed by adding additional vessels to further fractionate the base oil to form different viscosity cuts or stripping the base oil to reduce its viscosity.

[0201] Steam stripping can be utilized to reduce the vapor pressure at selected locations within the system. By reducing the vapor pressure, the operating temperature can also be decreased, thereby reducing the thermal energy required to maintain operation and the risk of fouling. Steam stripping can also assist in enhancing the yield and quality of useful oil products.

[0202] In the above embodiments, using stage 2, some high-quality base oil molecules are separated from the low-quality base oil molecules, thereby creating a first high-quality base oil stream in line 156 with low concentrations of aromatics, polar substances, unsaturates, heteroatoms, etc., and a second low-quality base oil stream 172 with high concentrations of aromatics, polar substances, unsaturates, heteroatoms, etc. Also, using a process similar to stage 3 described herein, some of the aromatics, polar substances, unsaturates, heteroatom molecules, etc. remaining in the high-quality base oil stream are converted to high-quality molecules to further purify, improve the saturation, and thereby produce a highly refined base oil, it is also possible to further upgrade the high-quality base oil stream. This oil may be suitable for use as white oil in the pharmaceutical or food processing industries and as a lubricating base oil in the industrial lubricating oil market.

[0203] In the embodiment shown above, the solvents recovered from the low-quality and high-quality base oils in lines 164 and 166 are combined and purified by removing water and other low-boiling contaminants in the solvent treatment and storage device 148 prior to reuse. Also, as known to those skilled in the art, the solvent can also be treated with a base or the like at this stage to neutralize the organic acids that may have accumulated in the solvent.

[0204] In different embodiments, a distillation system may be utilized to separate the base oil fraction from other used oil components. The treated used oil stream is heated to 250°F - 450°F, for example 300°F - 400°F, in a heater (such as heater 44), flows through a valve (not shown) into a flash distillation vessel (such as vessel 52), where a distillate stream (such as in line 54) is recovered from the used oil. The distillate stream can be burned as a process gas or condensed, separated from any water, glycol, etc., and used as fuel or the like. The discharged bottom stream can move to or be sent to an in-situ flash distillation vessel 70 and enter the oil pool at the bottom of the vessel. The oil pool can be maintained at a temperature of 400°F - 600°F, for example 450°F - 550°F, by being heated by a recirculation heater (not shown separately) (where the oil is sent out from the bottom of vessel 70, heated in a heat exchanger (such as heat exchanger 84), and returned to vessel 70). The flow rate of this recirculation stream can be sufficient to provide appropriate heat exchange in heat exchanger 84 to maintain the liquid layer (the oil pool at the bottom of the vessel) at the desired temperature, thereby producing the desired distillate fraction and maintaining turbulent flow and a high Reynolds number through the tubes of the heater.

[0205] The used oil stream entering from vessel 52 into vessel 70 can be heated by direct contact with this liquid layer, thereby evaporating the components of the used oil having a boiling point lower than that of the liquid layer and producing a distillate stream (in line 76). This distillate stream generally may have a boiling point in the range of about 350°F to about 500°F and can be condensed and used as fuel or the like. A portion of the bottom stream in line 82 may enter a third distillation vessel, such as vessel 90.

[0206] In some embodiments, the vessel 90 may be a distillation vessel that operates in a manner similar to the vessel 70 that uses a high-temperature liquid layer to heat the incoming flow by direct contact. The liquid layer of oil may be maintained at a temperature of 550°F to 750°F, such as 600°F to 700°F, by heating it through a recirculation heater 104 (where the oil is sent from the bottom of the vessel 90, heated by the heater 104, and returned to the vessel 90). A portion of the recirculation flow in line 102 may be diverted to the vacuum distillation vessel 112. A liquid layer with a liquid level 110 may be maintained at the lower part of the vessel 90. The vessel 90 can produce a distillate stream 96 having a boiling point in the range of about 500°F to about 650°F.

[0207] In the above embodiments, the vessels 52 and 70 may be operated at atmospheric pressure. These vessels can also be operated under high pressure or under vacuum, as known to those skilled in the art, and can achieve the separation of similar base oil fractions from used oil feedstock. The vessel 90 may be operated under negative pressure or under vacuum, for example, from full vacuum to about 500 mmHg, such as from 2 mmHg to 30 mmHg.

[0208] As illustrated in FIG. 2, the vessel 112 is typically a vacuum distillation vessel that can be operated under a vacuum in the range from full vacuum to 500 mmHg, such as 2 to 30 mmHg. The feed stream in line 106 from vessel 90 may be combined with the recycle stream in line 126 from the bottom of vessel 112 heated to 550°F to 700°F, such as 600°F to 650°F. The mass ratio between the two streams may be from 1:2 to 1:40 (the ratio of the flow rate of the feed stream to the flow rate of the recycle stream), such as 1:10 to 1:20. The distillate stream may be generated and pass through the distillate outlet 118. The distillate stream may have a boiling point in the range of about 650°F to about 1050°F. The liquid level 130 may be maintained in the vessel 112. The bottoms stream is discharged through line 120, moves through pump 122 to discharge line 124, and through discharge line 124, a portion of this stream is recovered as product. A portion of this stream may be returned via lines 126 and heater 128 and merged with the stream in inlet line 106. This heated bottoms stream can be used to maintain the desired feed temperature to vessel 112.

[0209] In one embodiment, it may be advantageous to add a stripping gas, such as vapor, to one or more of vessels 52, 70, 90, and 112 to strip light components from the oil and assist in the distillation and separation process. The stripping gas may be added at various points in the bottom half of the vessel, or may be added to the oil feed stream going to these vessels.

[0210] The solvent extraction column 140 may be any suitable stirred continuous flow liquid phase extraction column with a variable stirring speed that can be controlled without affecting the flow rate. The extraction solvent can be selected from ethanol, diacetone - alcohol, ethylene - glycol - mono(lower alkyl) ether, diethylene - glycol, diethylene - glycol - mono(lower alkyl) ether, o - chlorophenol furfural, acetone, formic acid, 4 - butyrol acetone, lower alkyl esters of lower mono - and dicarbonic acids, dimethylformamide, 2 - pyrrolidone and N - (lower alkyl) - 2 - pyrrolidone, N - methyl - 2 - pyrrolidone (NMP), epichlorohydrin, dioxane, morpholine, lower alkyl and amino(lower alkyl) morpholine, benzonitrile or di(lower alkyl) sulfoxide, and phosphonates, etc.

[0211] In some embodiments, N - methyl - 2 - pyrrolidone (NMP) may be used as the extraction solvent. The solvent extraction can be carried out at a temperature at which the extraction solvent and the oil in the feedstock are at least partially miscible, typically from about 100°F to about 250°F, preferably from about 130°F to about 190°F. Typically, both the solvent and the oil can be fed into the extraction column within this temperature range, but they do not need to be at the same temperature. The solvent dosage (the percentage of the solvent relative to the feedstock fed to the extraction column) is typically from 50 volume% to 1000 volume%, for example, from 100% to 500%. Typically, the solvent extraction is carried out in a vertical column, with the solvent fed at the top of the column and the purified used oil fed at the bottom. Water can be selectively injected into the solvent extraction column, if necessary, to control the solvent.

[0212] Similarly, a temperature gradient or in-zone heating or cooling can be used at various points along line 150 or throughout the solvent extraction column, affecting performance and selectivity. Also, recycling of both the raffinate and extract can be carried out at the same temperature or at different temperatures. In some cases, it may be beneficial to remove a sidestream from the extraction column, cool the raffinate stream or the extract stream, cool the sidestream, separate some of the solvent from the oil, and return the oil to the column. The solvent can be recovered from the raffinate stream in line 157 and the extract stream in line 155 using distillation. Distillation can be carried out by the action of the atmosphere or using a vacuum. By the action of the atmosphere, one or more flash separators, vacuum separators, multi-stage columns, etc., operated either under pressure or under vacuum, or combinations thereof, can be used to separate the solvent from the base oil. A guard bed suitable for use within the system described herein may include activated clay or spent catalyst.

[0213] The hydrogenation reactor 190 may comprise one or more hydrogenation catalysts having metal components from Groups V(b), VI(b) and VIII of the Periodic Table known to those skilled in the art. In some embodiments, compounds of nickel, molybdenum, vanadium, tungsten or cobalt metals supported on a carrier, such as activated carbon, diatomaceous earth, silica, alumina, etc., such as cobalt-molybdenum on alumina, nickel-molybdenum on alumina or nickel-tungsten on silica / alumina are used.

[0214] Additional processing may be carried out on the distillate stream in line 54 from vessel 52, for example, further separating components of this stream, such as water, glycol, solvent, light hydrocarbons, etc., thereby producing separate products, which may be used or further upgraded to high-quality products. Also, these product streams may be further processed to improve the quality as known to those skilled in the art.

[0215] In some embodiments, only one distillate fraction is withdrawn from vessel 112 for further processing in stage 2. Also, either a second fraction may be taken, or after vessel 112, another separation vessel (not shown) may be added to further fractionate the base oil distillate to produce base oils of different viscosity grades, etc., which can then be processed separately in stages 2 and 3.

[0216] Optionally, a phase transfer catalyst or the like may be used to enhance the operation in stage 2, thus enhancing the efficiency and selectivity of the process, whereby the separation of high-quality base oil molecules from low-quality base oil molecules is better achieved.

[0217] In the third stage of the process presented in the embodiments, it may be advantageous to operate reactors having a plurality of guard beds and arranged in parallel or in series, and to utilize phase separators or the like between each reactor or between the guard bed and the reactor. Further, in some cases, it may be advantageous to strip the base oil of light contaminants or to further fractionate it into fractions of different viscosities. Although the systems described herein do not utilize a hydrogen recovery system, it may be used to recover and purify unreacted hydrogen and reaction products after separation from the product base oil.

[0218] As described above, in the embodiments of the present disclosure, the base oil fraction is separated from the used oil feedstock, and then separated into a high-quality base oil stream and a low-quality base oil stream. Then, the low-quality base oil stream is upgraded to produce a base oil product with improved quality. The combination of these steps realizes an improved process and can address one or more of the problems described above.

[0219] The introduction of continuous-flow liquid-phase hydrogenation treatment in the final stage can supply a certain amount of excess hydrogen during the hydrogenation reaction, which can conveniently prevent or reduce catalyst coking. In addition, the introduction of the continuous-flow liquid-phase hydrogenation process eliminates the need to use a trickle bed in the final upgrading step, thereby avoiding the problem of fouling of conventional reactors in re-refining.

[0220] In addition, continuous flow liquid phase hydrogenation enables better control of the heat inside the reactor, helps maintain a steady temperature inside the reactor, thereby minimizing the need for large amounts of hydrogen gas to quench multiple catalyst beds and reactors.

[0221] It should be noted that the used oil may contain sludge and long-chain polymers that can be formed by the use and deterioration of engine oil or motor oil during use or in the re-refining process. The presence of these sludge and long-chain polymers can cause fouling and can affect the continuous operating time of the processing process at various stages. In the embodiments disclosed herein, these substances can be effectively handled and removed, thus reducing the risk of fouling and extending the continuous operating time of the processing process. For example, fouling in the CSU can be reduced by reducing the inner surface in the distillation vessel, reducing the rotating device, increasing the flow rate, or lowering the operating temperature, or a combination thereof. Recycling of the residue also helps maintain a high flow rate. By using staged distillation in flash and vacuum distillation vessels instead of a thin-film evaporator (TFE), in addition to the sequential removal of physical contaminants, more efficient separation and an increase in the yield of high-quality VGO, and a reduction in fouling can be achieved. Thus, a wider range of UMO feedstocks may be suitable for processing in the embodiments disclosed herein compared to conventional re-refining systems. The CSU embodiments disclosed herein can have a long on-stream runtime, for example, more than 6 months.

[0222] In some embodiments, the MSU can be used to separate long-chain lubricating oil molecules from short-chain or circular chain lubricating oil molecules. The long-chain lubricating oil molecules can be further refined to produce oil products, and the short-chain or circular chain lubricating oil molecules can be further processed in the MTU to form oil products.

[0223] The MTU embodiments described herein can be operated in continuous flow, but can also be operated in batch mode if desired.

[0224] Metals, phosphorus, silicon, and long-chain polymers present in the feedstock may remain in the raffinate stream from the MSU and, if they enter the hydrogenation reactor, can deactivate the catalyst and cause fouling at low flow rates, particularly in a gas-phase trickle-bed hydrogenation reactor. In the embodiments described herein, such negative aspects and problems can be reduced or avoided as described above.

[0225] Furthermore, the treated oil can be recycled back to the inlet of the hydrogenation reactor 190, enabling efficient use of hydrogen to maintain excess hydrogen within the reaction zone in the reactor. The recycle stream can also act as a heat sink, maintaining a more uniform and stable temperature in the reactor, thus enabling good temperature control and reducing the risk of coking in the reactor. The hydrogenation reactors described herein can be readily arranged and adapted to accommodate changes in the feedstock or spent oil being introduced.

[0226] It should also be noted that since a portion of the oil product (which can be up to two-thirds of the feedstock) has already been extracted and discharged from the MSU, the amount of liquid to be treated in the MTU is only a portion of the feedstock, for example, less than one-third.

[0227] In one embodiment, the method comprises: a) obtaining a feedstock comprising distillate; b) subjecting the feedstock to solvent extraction to obtain a high-quality base oil fraction and a low-quality base oil fraction; and c) subjecting the low-quality base oil fraction to a continuous-flow liquid-phase hydrogenation process to convert the low-quality base oil into a high-quality base oil fraction, ultra-low-sulfur diesel, and naphtha. In this embodiment, the distillate may have a boiling point of from about 500°F to about 1200°F. Prior to step b), the partially refined oil fraction may be subjected to oxidation, ozonation, acid treatment, or magnetic filtration. The distillate can be obtained by distillation of a used oil stream. The distillation may comprise: i) distilling the waste oil stream to separate at least some materials having a boiling point of less than about 350°F from the waste oil to produce a de-volatilized oil fraction and a light oil fraction; ii) separating at least some materials having a boiling point of greater than about 350°F and less than about 650°F from the de-volatilized oil fraction to produce a fuel oil fraction and a heavy oil fraction; and iii) separating at least some materials having a boiling point of from about 650°F to less than 1200°F from the heavy oil fraction to produce a partially refined oil fraction and a residue fraction. The used oil stream may be subjected to oxidation, ozonation, acid treatment, or magnetic filtration prior to distillation. In some embodiments, the distillate may also include distillate obtained from a crude oil upgrading process. Step c) may comprise: i) adding a solvent / diluent to the low-quality base oil fraction stream to form a continuous-flow liquid-phase diluent and feedstock mixture; ii) adding hydrogen to the diluent and feedstock mixture within a constant-pressure environment to form a mixture of continuous liquid-phase feedstock, diluent, and hydrogen; and iii) reacting the mixture of continuous liquid-phase feedstock, diluent, and hydrogen in the presence of a catalyst to remove predetermined compounds from the feedstock mixture, thereby converting the low-quality base oil into a high-quality base oil fraction, ultra-low-sulfur diesel, and naphtha.

[0228] In some embodiments, the continuous-flow liquid-phase hydrogenation process may be carried out in a reactor having, at a predetermined temperature, an upper zone of gas and a substantially larger lower zone of hydrogen dissolved in a liquid mixture surrounding the catalyst.

[0229] The light oil fraction can be separated from the de-volatile oil fraction by at least one of atmospheric distillation or vacuum distillation. The fuel oil fraction can be separated from the heavy oil fraction by at least one of atmospheric distillation or vacuum distillation. The partially refined fraction can be separated from the residual oil fraction by vacuum distillation in a non-packed column.

[0230] In some embodiments, the solvent extraction step may include the use of one or more solvents selected from ethanol, diacetone-alcohol, ethylene-glycol mono(lower alkyl) ether, diethylene glycol, diethylene-glycol mono(lower alkyl) ether, o-chlorophenol furfural, acetone, formic acid, 4-butyrol acetone, water, water-soluble salts, lower alkyl esters of lower mono- and dicarbonic acids, dimethylformamide, 2-pyrrolidone and N-(lower alkyl)2-pyrrolidone, N-methyl-2-pyrrolidone (NMP), mono- or polyprotic acids, mineral acids, carboxylic acids, hydroxide bases, carbonate bases, inorganic bases, epichlorohydrin, dioxane, morpholine, lower alkyl and amino(lower alkyl) morpholine, benzonitrile and di(lower alkyl) sulfoxide and phosphonates.

[0231] The extraction solvent may be N-methyl-2-pyrrolidone, optionally in combination with one or more additional solvents. The solvent extraction step can be carried out in an extraction column designed to limit entrainment and allow good separation of the oil and the extractant phase.

[0232] The saturation level, sulfur level, and VI of the base oil as shown herein are measured using the tests and analytical methods specified in Table E-1 of API 1509. Specifically, the saturation level is measured in accordance with ASTM International standard, ASTM D2007, the VI is measured in accordance with ASTM D2270, and the sulfur level is measured in accordance with one or more of ASTM D1552, D2622, D3120, D4294, or D4927.

[0233] As used herein, the term "about", when used with a numerical value, indicates that a variation of up to 10% in either direction from the specified value is allowed, unless otherwise specified.

[0234] Any range of values herein is intended to specifically include intermediate values or sub-ranges within any given range, and it should be understood that all such intermediate values and sub-ranges are individually and specifically disclosed.

[0235] Also, the words "a" or "an" mean "one or more" or "at least one", and it should be understood that any singular form herein is intended to include the plural form.

[0236] The term "comprise" (including all its variants) is intended to be open-ended and should be further understood to mean "including but not limited to", unless otherwise indicated by a contradiction.

[0237] In this specification, when a list of items is presented with "or" before the last item, any one of the listed items or any suitable combination of two or more of the listed items can be selected and used.

[0238] Of course, the above embodiments of the present disclosure are for illustrative purposes only and are not limiting. There is much room for change in the form of operation, the arrangement of parts, the details, and the order. The present invention is rather intended to encompass all such changes within the scope defined by the claims.

Description of the Reference Numerals

[0239] 5 System 10 Feedstock Container 12 Transport Line 14 Contaminant Separation Device 16 Outlet Line 18 Transport Line 20 Transport Line 22 Molecular Separation Device 24 Outlet line 26 Transport line 28 Transport line 30 Molecular processing device 32 Outlet line 42 Inlet line 44 Heater 46 Transport line 52 First flash distillation vessel 53 Top of the first flash distillation vessel 54 Transport line 56 Transport line 57 Bottom of the first flash distillation vessel 70 Second in-situ flash distillation vessel 72 Top of the second in-situ flash distillation vessel 74 Bottom of the second in-situ flash distillation vessel 76 Transport line 78 Transport line 80 Pump 82 Transport line 83 Transport line 84 Heater 86 Transport line 88 Liquid level 90 Third vacuum distillation vessel 92 Top of the third vacuum distillation vessel 94 Bottom of the third vacuum distillation vessel 96 Transport line 98 Transport line 100 Pump 102 Transport line 104 Heater 106 Transport line 108 Transport line 110 Liquid level 112 Fourth vacuum distillation vessel 114 Top of the fourth vacuum distillation vessel 116 Bottom of the fourth vacuum distillation vessel 118 Transport line 120 Transport line 122 Pump 124 Transport line 126 Transfer line 128 Heater 130 Liquid level 132 Heat exchanger 134 Transfer line 140 Stirred countercurrent liquid-liquid extraction column (solvent extraction column) 142 Bottom of the stirred countercurrent liquid-liquid extraction column (solvent extraction column) 144 Top of the stirred countercurrent liquid-liquid extraction column (solvent extraction column) 146 Contact part 148 Solvent system 150 Transfer line 152 Container 154 Solvent separation container 155 Transfer line 156 Transfer line 157 Transfer line 158 Top of the container 160 Bottom of the container 164 Transfer line 166 Transfer line 168 Top of the solvent separation container 170 Bottom of the solvent separation container 172 Transfer line 174 Heat exchanger 176 Diluent inlet 178 Guard bed 180 Top of the guard bed 182 Bottom of the guard bed 184 Contact zone 186 Transfer line 187 Mixer 188 Transfer line (hydrogen injection inlet) 190 Hydrogenation reactor 191 Upper zone of the first part 192 Catalyst bed of the first part 193 Lower zone of the first part 194 Upper zone of the second part 195 Catalyst bed of the second part 196 Lower zone of the second part 197 Upper zone of the third part 198 Catalyst bed of the third part 199 Lower zone of the third section 200 Transport line 201 Transport line 202 Stripper / sorter 204 Outlet line 206 Outlet line 208 Outlet line 300 Shovel extraction column 302 Vertical container 304 Lower inlet 306 Upper inlet 308 Upper outlet 310 Lower outlet 312 Two inlet / outlet parts for interface control 314 Two inlet / outlet parts for interface control 316 Baffle 318 Baffle 320 Agitator 322 Shaft 324 Speed changer 326 Turbine impeller

Claims

1. conducting continuous liquid-liquid solvent extraction by contacting a feedstock comprising refined used oil with an extraction solvent to produce an extract stream comprising the extraction solvent and an extract dissolved in the extraction solvent, wherein the feedstock and the extraction solvent are agitated by a variable speed agitator at a selected agitation speed during the solvent extraction; Separating the extract from the extraction solvent; subjecting the extract to a continuous flow liquid phase hydrogenation treatment to produce an oil product having a viscosity index of at least 80; A method comprising:

2. The liquid phase hydrotreating process comprises: adding a diluent to the extract to increase the solubility of hydrogen in the extract and form a liquid mixture comprising the diluent and the extract; adding hydrogen to the liquid mixture to dissolve the hydrogen in the liquid mixture; heating the liquid mixture with the dissolved hydrogen in the presence of a hydrogenation catalyst to saturate unsaturated materials in the liquid mixture and remove sulfur and aromatic materials from the liquid mixture and form the oil product; The method of claim 1 , comprising:

3. 3. The method of claim 2, wherein the extract comprises phosphorus and silicon, and the continuous flow liquid phase hydrotreating comprises removing phosphorus and silicon from the liquid mixture prior to exposing the liquid mixture to the hydrogenation catalyst.

4. 4. The method of any one of claims 1 to 3, wherein the extract comprises aromatics and the continuous flow liquid phase hydroprocessing comprises removing aromatics from the oil product.

5. 5. The method of claim 1, wherein the extraction solvent comprises n-methyl-2-pyrrolidone.

6. 6. The method of any one of claims 1 to 5, wherein the oil product comprises at least 90 wt% saturates.

7. 7. The method of claim 6, wherein the oil product comprises at least 95 wt% saturates.

8. 8. The method of any one of claims 1 to 7, wherein the oil product contains less than 0.03 wt% sulfur.

9. 9. The method of any one of claims 1 to 8, wherein the oil product has a viscosity index of at least 120.

10. 10. The method of claim 1, wherein the refined used oil comprises refined used motor oil.

11. 11. The method of any one of claims 1 to 10, wherein the refined used oil comprises refined used industrial oil.

12. 12. The method of any one of claims 1 to 11, comprising refining used oil to produce the feedstock.

13. 13. The method of claim 12, wherein said refining comprises subjecting said used oil to distillation to form said feedstock comprising a distillate from said distillation.

14. 14. The method of any one of claims 1 to 13, comprising forming a countercurrent flow of the feedstock and the extraction solvent in a solvent extraction column, wherein the agitation speed and flow rates of the feedstock and extraction solvent entering the solvent extraction vessel are independently adjusted based on the quality or nature of the feedstock.

15. a refinery configured to refine the used oil to form a feedstock comprising refined used oil; a continuous countercurrent liquid-liquid extraction column for extracting an extract from the feedstock using an extractant, the extraction column comprising an agitator configured to agitate the feedstock and extraction solvent passing through the extraction column at a variable agitation speed; a continuous flow liquid phase hydrogenation apparatus for hydrotreating the extract extracted by the extraction column to produce an oil product; Including, the system.

16. The continuous flow liquid phase hydrogenation apparatus comprises: a hydrogenation reactor containing a hydrogenation catalyst; a transfer line in fluid communication with the solvent extraction column and the hydrogenation reactor for transporting the extract from the solvent extraction column to the hydrogenation reactor; a diluent inlet on the transfer line for introducing a diluent into the extract passing through the transfer line to form a liquid mixture including the extract and the diluent; a hydrogen inlet on the transfer line downstream from the diluent inlet for introducing hydrogen into the liquid mixture; The system of claim 15 , comprising:

17. 17. The system of claim 16, wherein the liquid phase hydrogenator further comprises a guard bed located on the transfer line between the diluent inlet and the hydrogen inlet, the guard bed configured to remove at least phosphorus and silicon from the liquid mixture.

18. 18. The system of any one of claims 15 to 17, wherein the hydrogenation catalyst comprises palladium, gold, or nickel.

19. 19. The system of any one of claims 15 to 18, wherein the purification unit comprises one or more distillation columns.

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