Technology for rerefining used lube oils applied in Europe: a review

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ReviewReceived: 4 February 2013 Revised: 28 May 2013 Accepted article published: 7 June 2013 Published online in Wiley Online Library: 5 July 2013

(wileyonlinelibrary.com) DOI 10.1002/jctb.4137

Technology for rerefining used lube oilsapplied in Europe: a reviewAntonina Kupareva, Paivi Maki-Arvela∗ and Dmitry Yu. Murzin

Abstract

The European oil rerefining industry is comprised of 28 plants treating waste oil, which represent one-third in volume of thetotal European market for lubricants. The biggest European rerefineries with capacity greater than 40 000 tons/year applyvarious technologies for recycling of used oils from different sources. Used oil recycling technology has undergone significantchanges over the past decade. With the newly developed rerefining technologies it is possible to produce higher qualitybase oil compared with the traditional and old acid clay methods. Currently in Europe the following re-refining methods arewidely used: solvent extraction (N-methyl-2-pyrrolidone (Germany), Interline process (United Kingdom, Spain)); combinedvacuum distillation and solvent extraction (Vaxon process (Denmark, Spain); hydroprocessing (Hylube process (Germany));combined thin film evaporation and hydrofinishing (CEP process (Finland)); combined thermal de-asphalting and hydrofinishing(Revivoil process (Italy, Poland, and Spain)). The majority of applied technologies in Europe is appropriate for rerefining ofsynthetic lubricating oils, which currently are replacing the conventional mineral lube oils due to their enhanced performancecharacteristics. However, for the rerefining technologies applying alkaline treatment (CEP, Vaxon) and hydrofinishing step(Cyclon, Snamprogetti, Revivoil) the amount of synthetic or semi-synthetic oils based on esters in the feedstock should beeliminated, since these oils are less stable under alkali and hydrofinishing conditions.c© 2013 Society of Chemical Industry

Keywords: solvent extraction; hydrofinishing; used oil rerefining; base oil; thin film evaporation

INTRODUCTIONNowadays, there are a vast number of applications using lubeoils, such as internal combustion engines, vehicle and industrialgearboxes, compressors, turbines or hydraulic systems and others.The most important function of lubricants is the reduction offriction and wear. Mineral oil components continue to formthe quantitatively most important foundation of lubricants andrepresent mixtures of different types of hydrocarbons withaliphatic hydrocarbons predominant and chemical additives. Incontrast with mineral oil-based oils, that contain many differenthydrocarbons, and nitrogen-, oxygen-, and sulfur-containingchemical derivatives of these hydrocarbons, synthetic baseoils usually are prepared from a few well-defined chemicalcompounds, although in many cases based on petroleum also.Synthetic oils can be based on the following compounds:alkylated aromatic compounds, polybutenes, dibasic acid esters,polyalphaolefins, poly(alkylene glycol)s, neopentyl polyol esters,silicones, perfluoralkyl polyethers and several others. Similar tomineral base oil, synthetic base oils generally cannot satisfy therequirements of high performance lubricants without modernadditives. Moreover, some lube oil applications accept vegetableoils, which are biodegradable and contain long chain fatty acids intheir composition.

Nowadays, globally different automotive and industrial sourcesgenerate large amounts of used lubricating oils, which presenta serious pollution problem. Estimation of regional and globaldemands for lubricants demonstrated that Western Europeaccounts for only 13% of total worldwide demand, while NorthAmerica and Asia account for 22% and 30%, respectively, probablydue to the widespread use of automobiles compared with other

regions.1–4 Due to high lube oil consumption various countrieshave designed their own systems for management of waste oils.The rerefining industry has become an important industry in

many countries, such as USA,1–5 Australia,6 and Saudi Arabia.7

Worldwide there are about 400 oil rerefining plants using a varietyof technologies, with an overall capacity of 1.8 million tons/year.3

The ability to recycle waste oils is very closely linked to the oil’scomposition, level, type of contamination and of course economicaspects. There are about 200 oil recyclers in North America alone.3

Of these, only three are primarily rerefiners, which recover lubeoil for reuse. The others recycle waste oil by producing fuelfor burning/energy recovery. The number of rerefining plants inEurope is 28, of which 17 produce base oils.8 The industry has atheoretical nameplate capacity of 1.3 million tons correspondingto total turnover of between ¤ 200 and 250 million per year.8

According to European Commission resources,8–10 about 5.7million tons of lubricating oils are consumed in Europe annually,with automotive and industrial sectors accounting for 65% and35%, respectively. Such a scale of operation generates ca. 2.7million tons of used oil, or in other words around 48% of the totallube oil consumption. Of the latter quantity, only about 73%, or2.0 million tons, is collected, therefore approximately 0.7 milliontons or 23% is assumed to be lost or illegally burnt or dumped

∗ Correspondence to: Paivi Maki-Arvela, Abo Akademi University, ProcessChemistry Centre, Laboratory of Industrial Chemistry and Reaction Engineering,FI-20500 Turku/Abo, Finland. E-mail: [email protected]

Abo Akademi University, Process Chemistry Centre, Laboratory of IndustrialChemistry and Reaction Engineering, FI-20500, Turku/Abo, Finland

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Technology for rerefining used lube oils applied in Europe www.soci.org

Table 1. Overview of European lube consumption, used oil collection and recycling industry8

Country

Lubricants

consumption 2006,

tons×103/year

Collected

used oil 2006, %

Total used

oil capacity

2010, tons×103 Applied technologies Products

Germany 1174 45 798 HylubeMRD processAcid/clay treatment

and others

base oils + by-products; fuels

United Kingdom 800 44 50* Interline base oil + by-products

France 765 30 125 Ecohuile process base oil + by-products

Spain 545 29 184 InterlineVaxonRevivoiland others

base oil + by-products

Italy 542 40 303 RevivoilSnamprogettiAcid/clayand others


Poland 351 22 88* Revivoiland others


Netherlands 252 20 170 base oil + by-products, fuels

Belgium 142 42 40 Propak thermal cracking process gas oils, fuels

Greece 100 36 52 Cyclon and others base oil + by-products

Finland 79 29 60 CEP process base oil + by-products

Denmark 68 30 40 Vaxon base oil + by-products

*2009

in the environment. Engine oil represents more than 70% of thecollectable waste oil and industrial oils comprise the balance of30%. About 35% of the collected oil is rerefined into base oil; theremaining 65% is burnt replacing coal (10%), or used as heavy fueloil (45%) and unknown other products (10%). The available dataconcerning consumed, collected and rerefined lubricating oils inEuropean countries are summarized in Table 1.8

The main EU documents11–14 addressing used oil issues are theWaste Framework Directive (WFD), which was preceded by theWaste Oil Directive (WOD), the Waste Incineration Directive (WID)and the European Waste Catalogue (EWC). Waste oils are governedby Waste Framework Directive 2008/98/EC, especially by Article 21,which stipulates that Member States shall take necessary measuresto ensure that

• Waste oils are collected separately, where this is technicallyfeasible;

• Waste oils are treated in accordance with Articles 4 (wastehierarchy) and 13 (protection of the environment and humanhealth);

• Where this is technically feasible and economically viable, wasteoils of different characteristics are not mixed with each otherwith other kinds of waste or substances, if such mixing impedestheir treatment.

Due to the increasing necessity for environmental protectionand more and more strict environmental legislation the disposaland recycling of waste oils has become very important. Therecycling of waste lubricating oils can be accomplished with thefollowing different methods:15 used oil reprocessing, reclamationand rerefining. The products of used oil reprocessing and recla-mation are lubricating fluids with low quality requirements andheating and fuel oils, respectively, while rerefining of the used oilleads to production of valuable base oils with quality comparable

Figure 1. Flow diagram of the typical used oil rerefining process.

with virgin base oils. The principle of refining waste oils utilizes thefollowing four steps: dewatering and defueling, de-asphalting,fractionation and finishing process.16,17 The rerefining process isdepicted schematically in Fig. 1.

As mentioned earlier, the majority of collected lube oils inEurope is automotive oils. The main functions of lubricating oilsinclude reducing friction, carrying away heat, protecting against

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www.soci.org A Kupareva, P Maki-Arvela, DY Murzin

Table 2. Typical composition of lubricating oils18

Compound

Weight

percentage, %

Base oil 86

Viscosity index improvers (polyisobutylene,polymethacrylate)

5

Oxidation inhibitor (zinc dialkyl, dithiophosphate) 1

Detergent (barium and calcium sulphonates orphenates)

4

Multi-functional additives (dispersant, pour pointdepressant)

4

rust, protecting against wear and removing contaminants from theengine. All the above-mentioned properties are obtained owingto the package of additives carefully incorporated in appropriatequantities. A typical blend of lubricating oil is shown in Table 2.18

The separation of the lubricant base oils from additives, asphaltsand other contaminants contained in the used oil has beenperformed traditionally by distillation and acid/clay treatment,however, these traditionally applied technologies have beenbanned due to the following problems:

• Equipment fouling, in particular in the distillation equipment,reducing the operational time of the plant.

• Thermal cracking reactions reducing the yield and leading tolow quality base oils (colour, odour, unstability, etc.), which isdifficult to improve in the final treatment.

• Environmental difficulties due to the acid-clay waste disposal,emission of unpleasant odours and contaminated water.

To avoid thermal cracking and fouling, several processes havebeen developed, employing high vacuum (about 1 mbar) inthe distillation, thus separating asphalts and additives at lowertemperatures (falling film evaporator, short path distillation, etc.).As an alternative to the separation of asphalts and additives byvacuum distillation, extraction processes, using liquid solvents,have been developed (solvent de-asphalting). These processesoperate at near ambient temperatures, thus avoiding to a largeextent the equipment fouling problems and the cracking ofasphalts, additives and breakdown products since these areseparated before distillation of the lubricant bases.

Acid and clay treatment has been avoided in other processesby treating the distilled base oils with alkaline hydroxides orby catalytic hydrogenation. Modern processes combine thesetechnologies in different ways, trying to optimize investment andoperational costs, while producing a competitive quality product,

without creating environmental problems. Table 3 demonstratesthe key properties of used oils as well as the property changesthat occur after rerefining.15,19

The properties of rerefined used lube oils are similar to thefresh ones. The American Petroleum Institute (API) categorizedbase oils by composition (API Publication 1509) in 1993, as shownin Table 4. Modern regeneration technologies allow to producepremium quality base oils belonging to at least Group I accordingto the API base oils classification. Under more severe or solventfinishing conditions, Group II base oils could be obtained.20

This work overviews the available literature in waste oil recyclingtechnologies currently in use in European countries. It may,however, be noted that the technologies described do not coverall technologies applied in Europe, but only those that have acapacity higher than 40 000 tons/year with the primary task beingproduction of base oil. The majority of existing papers report onlythe main block schemes of processes without providing detailedinformation, which is often unavailable. Since, in today’s markets,the fractions of synthetic and semi-synthetic compounds usedhave increased significantly up to 30%,3 and keep on growing, theapplicability of currently used rerefining technologies is addressed.

DESCRIPTION OF DIFFERENT REREFININGPROCESS TECHNOLOGIESAcid-clay rerefining processThe acid-clay rerefining process was the first regeneration processcommercialized in the 1960s by many companies in the USA,wherein large amounts of sulphuric acid and clay were used totreat the waste oils.21 Acid-clay rerefining processes have beenwidely used by rerefining facilities. Used oil is pre-treated (pre-flash or vacuum distillation) for separation of water and lighthydrocarbons. Concentrated sulfuric acid (10–15 wt%) is addedinto dehydrated waste oil, wherein the foreign substances (e.g.additives and sulfides) will form sludge, enabling deposition within16–48 h which is thereafter separated from the waste oil. The

Table 4. API base oil categories

Group Sulfur, wt% Saturates, wt% Viscosity index

I >0.03 <90 80–119

II ≤0.03 ≥90 80–119

III ≤0.03 ≥90 ≥120

IV All polyalphaolefins (PAOs)

V All others not included in Groups I, II, III or IV

Table 3. Properties of used oils, intermediate products during rerefining15,19

Feed of hydrogenation Rerefined oil

Properties Used oil Feed of vacuum distillation light heavy light heavy

Water content, % 10 <1 <1 <1 — —

Density at 15◦C, kg m-3 ∼900

Kinematic viscosity at 40◦C, mm2 s-1 80

Flash point, ◦C >60 215 154 193 182 210

Total acid number, mg KOH g-1 <2.4 4.0 1.5 0.5 0.01 0.01

Sulfur content, mg kg-1 4000 4000 3000 3000 600 600

Zinc content, mg kg-1 650 650 <1 <1 <1 <1

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Figure 2. Block flow diagram of the acid-clay rerefining process adaptedfrom Refs 1,17.

impurities such as colloids, organic acids and waxy substances areremoved by clays (porcelain clay or aluminum silicate). Filtered oilis distilled to produce base oils with various characteristics andgas-oil. Figure 2 provides the flow chart of the process.

The base oil obtained has low quality with a lubricating yield of62–63% on dry basis.22 The product oils are dark in colour and tendto have a noticeable odour. Moreover, the products have from 4 to17 times higher content of polycyclic aromatic hydrocarbon (PAH)than virgin oils.

While the technology has relatively low capital costs andsimplicity of operations, as well as allowing production ofacceptable, although sub-standard, base oils, it also generatesacid tar, oil saturated clay, and other hazardous waste by-products.Under increasing environmental pressure this technology has beenbanned in most countries including many developing countries.Several plants with low capacity in Italy, Belgium and Germany stillemploy this technology8 (Table 1).

Hylube processGermany is the leader both in lubricants consumption andrerefining according to the European Re-refining Industry sectionof the Independent Union of the European Lubricants Industry(GEIR) data (Table 1). About 44% of the total used oil capacity goesto base oil production; the remainder is used for other productsincluding fuels, transformer oils, gasoil, etc. The Hylube processallows production of mainly base oils.

The HyLube process is a proprietary process developed byUniversal Oil Products (UOP) for the catalytic processing of usedlube oils into rerefined lube base stocks for reblending into saleablelube base oils.23 This is the first rerefining process in which asreceived used oil is processed, without any pretreatment, in apressurized hydrogen environment.

A typical HyLube process feedstock consists of a blend of usedlube oils containing high concentrations of particulate matter suchas iron and spent additive contaminants such as zinc, phosphorous,and calcium.21

A HyLube process unit has been successfully commercializedby Puralube GmbH located in Elsteraue / Zeitz, Germany, usingtechnology licensed to Puralube by UOP LLC. A simplified blockdiagram of the process is shown in Fig. 3. The first part ofthe process involves separation of the lube range and lightercomponents of the feed from the non-distillable residue portion.After the separation step the light feed is flowed through theso-called ‘guard’ reactor where metal-containing compounds andother impurities are accumulated in the large pore size catalyst.

Figure 3. Block flow diagram of the Hylube process adapted fromRefs 23–25.

The treated feed is hydrogenated in the main reactor before thesecond separation step. The Hylube unit operates with reactorsection pressures of 60–80 bar and reactor temperatures in therange 300–350◦C.24 As the feed is processed in hydrofinishingreactors, contaminants are removed and the quality of the lubebase oil is rejuvenated and enhanced. In addition to convertinghetero-atoms such as sulfur and nitrogen, the catalyst is able toincrease the viscosity index via saturation of multi-ring aromaticcompounds. After the hydrogenation, products are stripped andseparated in the fractionation tower to gasoline, petroleum, gasoil and base oil fractions. Light ends from the high temperatureseparator are blended with sodium carbonate and flowed to thelow temperature separator, where the waste water is settled andseparated. The hydrogen rich vapor from the cold separator isscrubbed, compressed, reheated and returned to the mixer.

The hydrocarbon liquids collected in the separators are sent tothe product fractionation section where the products are separatedinto various cuts to meet the desired lube oil viscosity grades.

The processed feedstock is converted into a wide boiling rangehydrocarbon product, which is subsequently fractionated intoneutral oil products of different viscosity to be used for lube oilblending. Due to hydrogenation the properties of three differentbase oil products are the same as the properties of fresh Group IIbase oils (Table 5).25 The Hylube process achieves more than 85%

Table 5. Properties of base oil products of Hylube-process15

Base oils

Properties

Light grade

(PUR- 75*)

Medium grade

(PUR- 160*)

Heavy grade

(PUR- 300*)

Density at 15◦C, kg m-3 850 855 860

Flash point, ◦C 190 215 228

Pour point, ◦C −12 −12 −12

Kinematic viscosity at40◦C, mm2 s-1

13.5 29.5 58


3.19 5.2 8.4

Viscosity index 100 115 116

Sulfur content, ppm 100 100 100

Saturates, %wt � 90 � 90 � 90

*Here and below Saybolt viscosities.


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lube oil recovery from the lube boiling range hydrocarbon in thefeedstock.

Mineralol Raffinerie Dollbergen (MRD) solvent extractionprocess using N-methyl-2-pyrrolidoneMineralol-Raffinerie is the best known and largest rerefinery inGermany, located near Hanover in an area with a distinctly ruralcharacter. This technology has been processing and recyclingused oil and oily liquids since 1955. Today, the refinery has thecapacity to process 230 000 tons/year of used oil and oil-containingliquids. Of these, 120 000 tons/year are used as feedstock for theproduction of 70 000 tons/year of new base oils.26

The applied oil rerefining process is based on a patent heldby AVISTA OIL.27 The ‘Enhanced Selective Refining’ process usessolvent N-methyl-2-pyrrolidone (NMP), which is commonly usedin the petroleum refining industry. NMP is a powerful, aproticsolvent with low volatility, which shows selective affinity forunsaturated hydrocarbons, aromatics, and sulfur compounds. Dueto its relative non-reactivity and high selectivity, NMP finds wideapplicability as an aromatic extraction solvent in lube oil rerefining.The advantages of NMP over other solvents are the non-toxicnature and high solvent power, absence of azeotropes formationwith hydrocarbons, the ease of recovery from solutes and its highselectivity for aromatic hydrocarbons. Being a selective solventfor aromatic hydrocarbons and PAH, NMP can be used for thererefining of waste oils with lower sludge, carbonaceous particlesand polymer contents, such as waste insulating, hydraulic andother similar industrial oils.28

The MRD solvent extraction process uses the liquid–liquidextraction principle. Figure 4 provides the flow chart of theprocess. Vacuum distillates from the flash distillation are usedas feed. These distillates are processed in a production cycle whichcan be adjusted to the quantity to be processed. Before thedistillate enters the extraction column, any residues of dissolvedoxygen in the distillate are removed in an absorber using steam.

Figure 4. Block flow diagram of the MRD Solvent extraction process usingN-methyl-2-pyrrolidone adapted from Ref 26.

Thereafter the distillate is sent to the bottom part of the extractioncolumn. As the distillate rises, undesirable aromatic hydrocarbonsand other contaminants are separated out by the counter-flowingheavier solvent, N-methyl pyrrolidone, which is fed in at the topof the extraction column. The solvent containing raffinate phaseleaves the extraction column at the top and is routed to thedownstream raffinate recovery section consisting of a distillationand a stripping column where the solvent is removed.

The extract phase is continuously withdrawn from the bottomof the extraction column, cooled down to a defined temperatureand separated in a separation drum from the separated secondaryraffinate. The latter is returned to the extraction column in order tooptimize the process yield. The extract phase from the secondaryseparation drum is sent to the extract recovery section wherethe solvent is removed. The extract recovery section also consistsof a distillation and a stripping column. The resulting extract isrouted to the offplot intermediate storage tank and used withinthe refinery as an energy carrier or mixing component for heavy oil.

The dry solvent separated in the distillation columns of theraffinate and extract recovery sections is returned to the solventtank. The moist solvent separated in the stripping columns of theraffinate and extract recovery sections is returned to the solventdrying column, where excess water is removed.

The average base oil yield within the process is about 91%.29

The base oils produced have high quality (Table 6).30 Theprocess is characterized by optimized operating conditions whichallow elimination of toxic polyaromatic compounds from thererefined base oil and preservation of the synthetic base oils likepolyalphaolefin (PAO) or hydrocracked oils, which are increasinglypresent in used oils.

Vaxon processThis technology is applied in the following two locations:

• a 40 000 tons/year plant in Denmark (Kalundborg);• a 42 000 tons/year plant in Spain (Barcelona – Taragona).

The process is an original Emprotec Vaxon technology. In2000 Avista Oil (USA) bought the licence of the process andcommercialized the process under the name of Avista Oil SolventExtraction –Vaxon Technology. This process contains chemicaltreatment, vacuum distillation and solvent refining units. Theadvantage of the Vaxon process is the special vacuum distillation,where the cracking of oil is strongly decreased (Fig. 5).21

Table 6. Properties of base oil products of MRD Solvent extractionprocess30

Base oils

Properties

Light grade

(KS 100)

Medium grade

(KS 150)

Heavy grade

(KS 200)

Density at 15◦C, kg m-3 852–856 857–860 860–865

Flash point, ◦C >220 >230 >230

Pour point, ◦C −12 −9 −9


22–26 32–36 40–46


4.4–4.9 5.5–5.6 6.4–7.1

Viscosity index 108–112 110–115 110–115

Sulfur content, wt% ≤ 0.25 ≤ 0.25 ≤ 0.25


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Figure 5. Vaxon process block flow diagram adapted from Refs 1,15, 31.

Used oil is chemically treated with alkali-hydroxides (sodiumand potassium hydroxide) for removal of chlorides, metals,additives and acidic compounds. The impurities can be bondedwith asphaltene molecules by these reactants, therefore theseimpurities can be easily separated from the oil.

After the chemical treatment the oil is separated to lightproducts, catalyst, base oil and residue. The feed is distillatedto two parts by a cyclonic column. Because of the formation oftangentially flowed thin film the light hydrocarbons are easilyand quickly distillated. The evaporated lighter part, consistingof light hydrocarbons (gas, diesel fuel) and water, is condensedin the upper part of the chamber, from where it is separated.The heavier oil part, circulating in the bottom, is heated, thusdecreasing heat transfer and decreasing coke formation inthe chamber.

The process can be carried out in several evaporators at varioustemperatures and pressure (i.e. from 160 to 345◦C and vacuumfrom 400 to 5 mbar) allowing separation of several oil cuts. Oilfrom the distillation can contain some undesirable componentsand should be additionally treated.

The polycyclic aromatic hydrocarbons are separated by solventrefining with polar solvents (dimethyl-formamide, N-methyl-2-pirrolidone, etc.). This is carried out in a multi-stage extractor,which is followed by solvent recovery from both phases. Thetreated raffinate can be additionally distilled to obtain variousbase oil cuts with yields of 65–70%.12 The polycyclic aromatichydrocarbons, which concentrate in the extract, are used for heatenergy production or as bitumen blending component.

The chemical final stage does not, however, allow the productionof high quality base oils; although in Spain the Cataloniarefinery produces basestocks accepted by an original equipmentmanufacturer (OEM).

As mentioned above, the technology belongs to Avista Oil,which is one of the biggest producers of rerefined base oils in

Figure 6. Block flow diagram of the CEP process adapted fromRefs 21,32, 33.

Europe. Germany-based Avista has three rerefiniries in Europe,Mineralol-Raffinerie Dollbergen GmbH in Dollbergen, Germany,Dansk Olie Genbrug A/S in Kahlundborg, Denmark and the NorthRefining and Trading N.V., Netherlands. Furthermore, Avista Oilholds a majority holding of about 75% in the Dutch rerefiningmarket since August 2012. In connection with this fact, the lubedistillate obtained from the Vaxon process (Denmark) or NorthRefining (Netherlands) are precursors for the Avista Oil base, theproperties of which are listed in Table 6.

CEP processThe process was designed by Chemical Engineering Partners (CEP),a process technology company offering a range of products andservices for rerefining waste lubricating oils. The CEP process islocated in Hamina, Finland and has a capacity of 60 000 tons/yearwith base oil production of 42 000 tons/year.

The process combines thin film evaporation and hydropro-cessing (Fig. 6). The used oil is chemically pretreated to avoidprecipitation of contaminants which can cause corrosion andfouling of the equipment. The pretreating step is carried outat temperatures from 80–170◦C. The chemical treatment com-pound comprises sodium hydroxide, which is added in a sufficientamount to give a pH about 6.5 or higher.32 The pre-treated usedoil is first distilled for separation of water and light hydrocarbons.Water is treated and sent to a waste water treatment facility. Lighthydrocarbons are used at the plant as fuel or sold as a product.Thereafter, free-of-water oil is distilled under high vacuum in a thinfilm evaporator for separation of diesel fuel, which can be used atthe plant or sold as fuel. Heavy materials such as residues, metals,additive degradation products, etc. are passed to a heavy asphaltflux stream.

The distillate is hydropurified at high temperature (315◦C) andpressure (90 bar) in a catalytic fixed bed reactor.37 This processremoves nitrogen, sulphur, chlorine and oxygenated organiccomponents.

In the final stage of the process, three hydrotreating (Hydrofin-ishing) reactors are used in series to reduce sulfur to less than300 ppm and to increase the amount of saturated compounds toover 95%, in order to meet the key specifications for API Group II


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Table 7. Properties of base oil products of CEP process34

Properties Medium grade (Base oil - N150)

Density at 15◦C, kg m-3 840–860

Flash point, ◦C >200

Pour point, ◦C <−9

Kinematic viscosity at 40◦C, mm2 s-1 26–32

Kinematic viscosity at 100◦C, mm2 s-1 5–6

Viscosity index >110

Sulfur content, ppm <300

Saturates, %wt >95

base oil (Table 7). The final step is vacuum distillation to separatethe hydrotreated base oil into multiple viscosity cuts in thefractionator.

Hydroprocessing technology is one of the most widely useddistillation processes to eliminate undesirable components suchas sulphur, nitrogen, metals or unsaturated hydrocarbons. Theyield of base oils is about 70%.34

Ecohuile processEcohuile claims to rerefine about 125 000 tons of used oil annuallyon the Lillebonne site, recycling 45% of the used motor oilscollected in France. The recycled oil corresponds to 10% of thebase oil market in France.

The rerefining process was based on vacuum distillation andacid-clay treatment steps until the end of 2000.35 Clay adsorptionwas banned on 1 January 2001 and the plant was modified andupgraded to the Sotulub process.36 Moreover, the addition ofinjection facilities of so-called Antipoll-additive (1–3 wt% of puresodium hydroxide) has been provided and has allowed solving thefollowing basic problems:

• corrosion of dehydration column and cracking column topsection due to the organic acidity of the used oil;

• plugging of equipment and piping due to polymer formation inthe cracking section;

• high losses of base oil in the oily clay due to the highconsumption of clay.

The Sotulub proces37 is based on treatment of the used oilwith an alkali additive called Antipoll and high vacuum distillation(Fig. 7). The used oil is pre-heated to about 160◦C and mixed witha small amount of Antipoll-additive, which decreases equipmentfouling. In the next step, oil is drawn into the flash-drum wherewater and light hydrocarbons are separated from the lubricatingbase.

The dehydrated oil is additionally heated to 280◦C and strippedunder vacuum to remove the gas-oil fraction. Thereafter oil isdistilled under high vacuum in a thin-film evaporator. In theprocess asphaltic residue, containing heavy metals, additives,polymers and degraded products, is separated from the bottomof the column.

Distilled oil is condensed and treated again with a small amountof Antipoll to eliminate all traces of undesirable compounds.This allows a final product to be obtained with acceptablequality without any additional finishing stage. Oil is additionallyfractionated to obtain various base oil cuts.

The process provides base oils with a yield of 82–92%.36 Theproperties of the product base oils are listed in Table 8.

Figure 7. Block flow diagram of the Sotulube process adapted from Ref 1.

Table 8. Properties of base oil products of Ecohuile process36

Base oils

Properties

Medium grade

SN 150

Heavy grade

SN 400

Flash point, ◦C >200 >230

Pour point, ◦C <−6 <−6

Kinematic viscosity at 40◦C, mm2 s-1 27–33 76–85

Metal contents, ppm <0.5 each <0.5 each

Cyclon processThe process licence belongs to Kinetic Technology International(KTI).38 The industrial plant to implement the KTI Relube processwas built in Greece for LPC in 1982.35 Greek Cyclon Hellas Companycurrently uses this technology with an annual capacity of 40 000tons.

The process flow diagram of the Cyclon process is illustratedin Fig. 8. Used oils taken from storage tanks are dewatered andthe light hydrocarbons are removed by distillation. The heavierfraction is sent to high vacuum distillation, where the majority ofbase oil components are evaporated from the heavy residue. Theoils in the residues are extracted with propane in the de-asphaltingunit and sent to the hydroprocessing unit where the other oils areprocessed. Then they are treated with hydrogen and fractionatedbased on the desired base oil features.

The rerefined base oil products have high quality due to thehydrogenation.39,40 Information on the physical properties of theobtained oils is not available in the literature.

Revivoil processThe Revivoil process was developed jointly by Axens andViscolube41 in Viscolube facilities. Currently the Revivoil process isapplied in the following locations:

• a 130 000 tons/year plant in Italy (Pieve Fissiraga);• a 80 000 tons/year plant in Poland (Jedlicze);• a 59 000 tons/year plant in Spain (Huelva).


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Figure 8. Flow diagram of the Cyclon process block adapted fromRefs 1, 20.

Figure 9. Block flow diagram of the Revivoil process adapted fromRefs 1, 15, 42.

Revivoil process is made up of three key sections: preflash,thermal de-asphalting and hydrofinishing (Fig. 9).42 The filteredused oil from storage tanks is heated to 140◦C and then distilledin a preflash column where the water and light hydrocarbons areseparated.

The dehydrated oil is distilled at 360◦C in vacuum in a thermal de-asphalting unit (TDA), where the oil is separated from substancesthat can enhance fouling in an intermediate tank. The asphalticand bituminous products remain at the bottom and three side cutsof different viscosities are obtained at the same time. Intermediategas oil is collected from the top of the column.

For improvement of the product quality, oil cuts after TDAare treated with hydrogen over the catalyst. The hydrofinishingprocess starts in a fired heater where the oil and hydrogen areheated to 300◦C. They are then sent to a reactor containing acatalyst favouring hydrogenation of the unsaturated compounds,as well as sulphur and nitrogen containing compounds. The reactoreffluent is then separated into two phases, the vapour phase andthe liquid phase; the first one is washed with water to remove thechlorine and sulphur compounds, the second one is stripped withsteam to eliminate the most volatile compounds and restore theflash point. The water contained in the oil after stripping is thenremoved in a vacuum dryer.

The yield of base oils from the Revivoil process is about 72%.12

According to the operating parameters of hydrofinishing, the finalbase oil quality can be upgraded until the amounts of sulphur

Table 9. Properties of base oil products of Revivoil process43

Base oils

Properties

Light

grade

Medium

grade

Heavy

grade

Density at 15◦C, kg m-3 852 853 858

Kinematic viscosity at 40◦C, mm2 s-1 16.5 30.6 55.2

Kinematic viscosity at 100◦C, mm2 s-1 3.6 5.3 7.8

Viscosity index 101 106 107

Sulfur content, wt ppm <300 <300 <300

and saturated compounds fulfil the API Group II requirements(Table 9).43

Snamprogetti process/ IFP technologyThe process technology was developed by the ‘Institut Francais duPetrole’ and is also known as the Selecto Propane Process.44 Oneplant of 84 000 tons/year capacity is working with this technologyin Ceccano, Italy.

The Snamprogetti process combines vacuum distillation andhydrogenation including a propane extraction step before andafter vacuum distillation (Fig. 10). The extraction technology issimilar to the one carried out in crude oil refineries to separate outasphaltenes.

In the first stage of the Snamprogetti technology, the lighthydrocarbons and water are removed by atmospheric distillation.In the second stage, all the impurities picked up by the engineoil, including the additives and partly degraded polymers, areremoved by extraction with propane in the temperature range75–95◦C in a propane de-asphalting section (PDA I). After strippingthe propane, the oil is heated again and vacuum distilled at atemperature of 300◦C. In this stage lubricating bases having lowerviscosity and free of impurities are separated. The vacuum residueis then heated to 300–450◦C under adiabatic conditions and sentto the second extraction stage (PDA II) in which metal contentand asphaltic components are further reduced. After extraction,propane is stripped and recycled in the process. The base oil cutsfrom the vacuum residue (bright stock) are finally hydrogenatedto improve the colour and to increase the oxidation stability of thebase oils.

Figure 10. Snamprogetti process block flow diagram adapted fromRefs 42, 45.


17

88


Figure 11. Block flow diagram the Interline process adapted fromRefs 1, 21, 42.

Products from the Snamprogetti process have high quality dueto the final hydrofinishing. Moreover, the yield of the base oils ishigh, approximately 74–80%.12,20

Interline processInterline Hydrocarbon INC., a Utah based company, has developeda propane extraction process for used oils with a clay treatment.35

In 2001, Interline patented an improved extraction technologyincluding a pretreatment of the used oil with chemicalsand catalysts, which increased the selectivity of the propaneextraction.46

Interline proposes a process based on propane de-asphaltingat ambient temperature and under a pressure that facilitatesseparation in the liquid phase. The Interline process is applied inthe following locations:

• a 36 000 tons/year plant at Fuenlabrada, Spain;• a 50 000 tons/year plant at Stoke-on-Trent, United Kingdom.

The Interline process is depicted in Fig. 11. The used oil is pre-treated with a basic solution containing ammonium hydroxideand/or potassium hydroxide for neutralization of undesirablecompounds. Pre-treated in this way, oil is mixed with propane,which has a high selectivity for hydrocarbons, and then sent to thesolvent mixing and extraction vessel. Most of the additives, waterand other insoluble compounds are separated from the propane-base oil mixture. The solids and water settle to the bottom andenter the residue–water separator where water is separated froma tar-like material which goes to the asphalt blending tank. In thistank, the tarlike material is blended with the vacuum distillationresidue to produce an asphalt extender-modifier product. Thewater is purified and returned to the environment. The solvent–oilmixture is pumped to an oil–solvent separation system. Thepropane is re-condensed with cooling water and returned to thesolvent vessel. Solvent-free oil is then stripped to remove lighthydrocarbons and the remaining propane. The flash adjustedoil is then directed to a traditional vacuum distillation column.The distilled lubricant oil product is a base oil (Table 10), whichis classified as group I according to API Publications, although,by saturates content (91–92%) and viscosity index (>100), theproduct oil could be considered in group II (Table 4).47

Table 10. Properties of base oil products of Interline process47

Base oils

Properties

Medium grade

SN-150

Heavy grade

SN-300

Flash point, ◦C 235 245

Pour point, ◦C −9 −9

Kinematic viscosity at 100◦C, mm2 s-1 5.0–5.5 7.5–8.0

Viscosity index >100 >100

Saturates, %wt >91 >91

The lubricating oil yield declared for the Interline processis 79%.22,48 The extraction process removes the majority ofadditives. The Interline process is interesting from the economicspoint of view because it eliminates thin film distillation and theneed for hydrogenation. Both investment and maintenance costsare low.

The drawbacks of the Interline process are that the feed shouldnot contain polychlorinated biphenyls (PCBs), and its chlorinecontent should be below 1000 ppm, since this process has no finalhydrofinishing step.

Propak thermal cracking processIn Belgium, used oil is treated not at a rerefinery designed tomanufacture base oil but at a cracking plant operated by SITA thatmanufactures, among other products, gasoil. The market for gasoilis very large and thus selling the modest quantity output fromthe plant presents no difficulties compared with those confrontedby vendors of rerefined base oils.49 The Propak technology wasdeveloped in the United States, offered under licence by PropakSystems Ltd, Canada. This technology was installed in Belgium bythe end of 2001 with plant capacity of 40 000 tons/year operatedby WATCO.

Propak thermal cracking technology allows production of gasoils or fuels. A block flow diagram of the Propak process is depictedin Fig. 12.

The Propak process consists of screening and dewateringsections, followed by a thermal cracking section, a separationor distillation depending on the product state desired and finallypurification and stabilization stages. The used oil is passed tothe cracking section which consists of a fired process heater anda thermal cracking section. The product is heated and exposedto appropriate pressure, temperature, residence time and otherconditions that favor the transformation of the used oil to gasoilboiling range hydrocarbons. The cracking section discharges a hotheavy residual product that concentrates ash, heavy metals andother undesirable components.

The vaporized hot gas stream, from the thermal cracking section,contains a mix of light hydrocarbons. The hot gas stream proceedsto the distillation or separation stage in which the lighter boilingrange naphtha is separated from the gasoil. In certain plantconfigurations, a heavy boiling fraction is recycled back to the firedprocess heater. Gasoil in the liquid state is led to the stabilizationsection from distillation.

Propak technology is characterized by a large operationaland product flexibility. Process operating conditions (tem-perature, pressure, residence time) can be varied to pro-duce a desired product such as heavy fuel oil, gasoil orbase oil.


17

89


Figure 12. Block flow diagram the Propak thermal cracking processadapted from Refs 1, 21.

BASIC PRINCIPLES OF THE LATESTTECHNOLOGIES FOR USED OIL REREFININGNowadays due to different treatment and finishing methods,there are currently available many new technologies,50 such asthin film evaporation (TFE), including combined TFE and clayfinishing, TFE and solvent finishing, TFE and hydrofinishing,thermal de-asphalting (TDA), TDA and clay finishing, and TDA andhydrofinishing. In addition, solvent extraction and hydrofinishingare being developed by means of hydrofinishing after the solventde-asphalting process.

Thin film evaporation technology includes a rotating mechanisminside the evaporator vessel which creates high turbulence andthereby reduces the residence time of feed-stock oil in theevaporator. This is done in order to reduce coking, which is causedby cracking of the hydrocarbons due to impurities in the used oil.Cracking starts to occur when the temperature of the feedstock oilrises above 300◦C. However, any coking which does occur will foulthe rotating mechanism and other mechanisms such as tube-typeheat exchangers are often found in thin film evaporators.

Solvent extraction processes are widely applied to removeasphaltic and resinous components. Low molecular weighthydrocarbons as solvents selectively dissolve the undesiredaromatic components, the extract, leaving the desirable saturatedcomponents, especially alkanes, as a separate phase, the raffinate.Liquid propane is by far the most frequently used solvent forde-asphalting residues to make lubricant bright stock, whereasliquid butane or pentane produces lower grade de-asphalted oilsmore suitable for feeding to fuel-upgrading units.

The liquid propane is kept close to its critical point and, underthese conditions, raising the temperature increases selectivity. Atemperature gradient is set up in the extraction tower to facil-itate separation. Solvent-to-oil ratios are kept high because thisenhances rejection of asphalt from the propane/oil phase. Counter-current extraction takes place in a tall extraction tower, of the typeshown in Fig. 13. Typical operating conditions are the following:53

Figure 13. A block flow diagram the typical solvent extraction unit adaptedfrom Ref. 53.

• propane/ feedstock volume ratio from 5–10:1• pressure 25–35 bar• top temperature 60–80◦C• bottom temperature 30–40◦C.

Recent studies showed that propane can be replaced byan alcohol–ketone mixture, which reduces coking and foulingproblems during distillation.51,52 The solvent chosen should meetthe following requirements: maximum solubility for the oils andminimum solubility for additives and carbonaceous matter; abilityto be recovered by distillation. New plant units increasingly useN-methylpyrrolidone because it has the lowest toxicity and can beused at lower solvent/oil ratios, saving energy.

Independent of the contacting method used, the end resultis two product streams. The raffinate stream is mainly extractedoil containing a limited amount of solvent, while the extractstream is a mixture of solvent and aromatic components. Thestreams are handled separately during solvent recovery andthe recovered solvent streams are recombined and recycled withinthe plant. Solvent recovery is an energy-intensive part of thesolvent extraction process.

For several years, catalytic hydrotreatment stood out as themodem and successful refining treatment from the point of viewof the yield and quality of the finished products. Hydroprocessing ismore often applied as a final step in the rerefining process in orderto correct problems such as poor colour, oxidation or thermalstability, demulsification and electrical insulating properties. Asimplified flow diagram of a hydrofinishing plant is shown in Fig. 14.Oil and hydrogen are pre-heated and the oil allowed to trickledownwards through a reactor filled with catalyst particles wherehydrogenation reactions take place. The oil product is separatedfrom the gaseous phase and then stripped to remove traces ofdissolved gases or water. Typical reactor operating conditions forhydrofinishing are the following:53

• catalyst temperature, 250–350◦C,• operating pressure, 20–60 bar.

The following reactions can be operative: hydrorefiningreactions with the objective of removing heteroelements and tohydrogenate olefinic and aromatic compounds, and hydroconver-sion reactions aiming at modifying the structure of hydrocarbonsby cracking and isomerization.35 Hydrotreatment catalysts aremade of an active phase constituted by molybdenum or tungstensulfides as well as by cobalt or nickel on oxide carriers.

Generally applied combinations are Co-Mo, Ni-Mo, and Ni-Wfor the active phase and high surface area γ -alumina (transition


17

90


Figure 14. Flow diagram of hydrofinishing unit adapted from Ref 53.

alumina) carrier. The metal content, expressed as oxides canreach 12–15 wt% for Mo and 3–5 wt% for Co or Ni. Co-Mocatalysts are preferentially used for hydrodesulphurization and Ni-Mo for hydrogenation and hydrodenitrogenation. Ni-W catalystsare applied for low-sulphur feeds. The most-used carriers arealumina and alumina-silica, the latter being characterized bya higher cracking activity.35 The currently applied catalysts inrerefining are modified in order to improve the product baseoil quality and to decrease the coke formation, however, theircomposition is typically not disclosed in the open literature.

The technologies applying hydroprocesses require relativelyhigh investments compared with others. However, dependingon the technology adopted, the total cost might be lower thanin solvent extraction process due to the high operating coststo make up for the solvent losses. On the other hand, solventextraction and chemical treatment processes do not requirecatalyst regeneration. Moreover, it is not necessary to establish ahydrogen gas supply facility in these methods which in additionreduces a risk concerning operation safety.

COMPARISON OF APPLIED TECHNOLOGIESThe currently applied technologies can be compared in terms ofoperating and capital costs, quality of feedstock and productsobtained. The technologies described can be divided into thefollowing groups:

1 Solvent extraction process2 Hydroprocessing

Combined processes:

3 Vacuum distillation or thin film evaporation and finishingprocess (solvent extraction or chemical treatment)

4 Thin film evaporation and hydrofinishing5 Thermal de-asphalting and hydrofinishing6 Solvent extraction and hydrofinishing

The advantages and drawbacks of the processes currentlyapplied in European rerefining are summarized in Table 11. Generaladvantages for solvent extraction processes, such as MRD solventextraction and Interline processes are the following:

• Toxic PAH and PAN are completely eliminated;

• All of the synthetic base oil compounds, such as polyalphaolefin(PAO)/hydrocarbon oils are preserved;

• The process requires relatively low pressure and temperature;• Used solvents are recyclable;• The amount of waste produced is insignificant.

The drawback of solvent extraction technology is the depen-dence of the product oil quality on the quality of the feedstock,since this process is a physical one and does not involve anychemical reactions with formation of the desired hydrocarbonstructures. The process leads to diminishing concentrationsof polychlorinated biphenylenes, aromatic compounds andspecifically polycyclic aromatic hydrocarbons, which were formedduring the oil use. Thereby the solvent extraction technologyallows the production of the re-refined oil bases of the same butnot superior quality to the feedstock base oils.

The MRD process belongs to the new generation processes,where NMP is applied as a solvent instead of propane as usedin the Interline process. NMP has a lower toxicity and a higherselectivity to the undesired species than propane. Moreover NMPcan be used at lower solvent–oil ratios, saving energy, thus, theMRD process can be more economically attractive than Interline.The MRD process demonstrates higher yield of the product oilof about 91% than the product yield in Interline process whichis c. 79%. The quality of MRD-product oils is slightly higher thanInterline-oils, the viscosity indexes are about 110 and 100 in MRDand Interline processes, respectively. Since the Interline processcontains alkaline pretreatment of used oil, the amount of vegetableand some types of synthetic oils should be eliminated due to theirinstability under alkaline conditions.

Vaxon and EcoHuile (Sotulub) processes are based on thevacuum distillation of oil cuts in thin film evaporators, which reducecoking caused by cracking of the hydrocarbons and oil impuritiesat high temperatures. Both processes apply alkaline pretreatmentof the used oils, which requires the elimination of synthetic andvegetable oils in the feedstock. The Vaxon process has an additionalfacility of solvent extraction treatment, which allows generation ofproduct oils with higher quality compared with Ecohuile-products.Nevertheless, the quality of products is worse than in the abovesolvent extraction processes. In order to produce high qualitybase oils finishing steps should be added in these technologies,however such revamps will increase operating and capital costsand the processes could become less financially attractive.

Hydrofinishing processes are applied in such technologies asHylube, CEP, Revivoil, Snamprogetti and Cyclon processes. Theadvantages of these technologies are listed below:

• High yield and quality of products independent of the feedstockproperties;

• Efficient elimination of chlorides.

However, the hydroprocessing technologies have the followingdrawbacks:

• High pressure and temperature;• A need for hydrogen gas supply facility;• High safety standards;• High operating and capital costs;• Low operational efficiency;• A need for feedstock analysis and pretreatment;• A necessity for catalyst regeneration.

Hylube technology applying hydroprocessing allows produc-tion of high quality base oil products, in which viscosity index is


17

91


Tab

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17

92


higher than 110 and sulfur content is less than 100 ppm. The pro-cess feedstock is oils from different sources, however, a key factorin maintaining stable Hylube catalyst activity is minimization ofthe inorganic contaminants level in the reactor feed. Thus, carefulmonitoring of the used oil for known catalyst poisons such asarsenic and silicon is needed, moreover, some synthetic oils thatare unstable in hydroprocessing conditions should be eliminated.The high quality of the products obtained is compensated byrelatively high capital investment and operating costs.

The CEP process, which is a combination of TFE and hydrofinin-shing step, produces high quality product oils comparable withHylube-products. Since this process applies caustic pretreatmentof the used oil, the amount of vegetable oils and some types ofsynthetic oils should be eliminated. Off-site catalyst regenerationcauses an increase in the operating and capital costs.

The Revivoil process accepts all type of used oils. Thermal de-asphalting combined with hydrofinishing allows generation ofhigh quality products with a yield of about 72%. The advantage ofthis technology is regeneration of the used catalysts.

The advantage of processes applying solvent extractioncombined with hydrofinishing (Snamprogetti and Cyclon) is itsacceptance of all types of used oil. Similar to all technologiesapplying hydroprocessing the product oil quality is high withyields of c. 72–80. Drawbacks are high operating and capital costs,since both technologies use propane, which belongs to the oldgeneration of solvents. Propane requires high solvent–oil ratios,which increases energy consumption; moreover losses of propanein the Snamprogetti process are about 5–10%.

In terms of the qualities of the feedstock required to obtain thedesired product, high quality base oils API Group II/II+ can beobtained by solvent extraction methods only when the reactionmixture is homogeneous. Therefore the quality of the base oilproduced with this technology is directly related to the qualityof feedstock, while hydrofinishing technology allows base oil APIGroup II to be obtained independently of the quality of thefeedstock. The major drawback of hydroprocessing is the catalystsensitivity and poisoning; in this regard feedstock pretreatment isnecessary to prevent catalyst deactivation. However, technologiesapplying alkali treating agents (CEP, Vaxon, Ecohuile and Interline)cannot be used for rerefining vegetable and some types ofsynthetic oils. Thus, the yield and selection of the operationconditions are strongly dependent on the composition andproperties of the feedstock.

CONCLUSIONSThe lube oil consumption in Western Europe accounts for 13% ofthe total worldwide consumption, which is about 5.7 million tonsannually. According to GEIR sources,8 about 2.7 million tons/yearof waste oil are generated as a result of lube oil usage. Europe is theleader in waste oil recycling; the total European rerefining industryhas a theoretical nameplate capacity of 1.3 million tons. The realannual waste oil treatment accounts for 0.7 million tons/year,whereas worldwide overall capacity is 1.8 million tons/year.

Today the European waste oil recycling industry is comprisedof 28 plants. Seventeen of them produce base oils with yieldhigher than 70%. Under increasing environmental pressure acid-clay treatment, which was the first oil regeneration process used,was substituted in the majority of European countries with newtechnologies based on solvent extraction and hydroprocessing.Leading industrial processes employ different technologies, suchas combined thermal de-asphalting and hydrofinishing (Revivoil),

solvent extraction (MRD process, Interline), solvent extractionand hydrofinishing (Cyclon, Snamprogetti), thin film evaporationand different finishing process (Ecohuile, Vaxon, CEP) andhydroprocessing (Hylube).

The technologies applying hydroprocessing obtain product oilswith the highest quality independently of the quality of feedstock.Thus technologies such as Hylube, CEP, Revivoil, Snamprogettiand Cyclon produce high-quality base oils, which fulfill the APIGroup II and even II+ requirements. In terms of the nature of thefeedstock, some synthetic oils which have enhanced performancecharacteristics and currently are replacing conventional minerallube oils, can be regenerated along with mineral oils. Others (basedon esters for instance) are less suitable for regeneration becausethey tend to be less stable to the hydrofinishing step. Moreover,these processes require high operating and capital costs. Catalystpoisoning is also one of the drawbacks of hydroprocessing. Inthis regard feedstock should be carefully monitored to estimatecatalyst poisons and thereafter the feedstock should be pretreatedto prevent catalyst deactivation. The alkaline pretreatment of usedoils is a commonly used process, however, taking into accounta trend towards more synthetic or semi-synthetic compoundsin lubricants, the use of alkali agents can cause problems duringrerefining some types of synthetic oils (based on esters for instance)which tend to be less stable in the presence of alkali agents.Thus, technology applying alkali treating agents (CEP, Vaxon,Ecohuile and Interline) cannot accept vegetable and some typesof synthetic oils for rerefining, whereas technologies applyingsolvent extraction are independent of the feedstock nature and canprocess used oils from different sources. The drawback of solventextraction is dependence of the product quality on hydrocarbonfeedstock composition. The high quality base oils API GroupII/II+ can be obtained by solvent extraction methods only whenthe reaction mixture is homogeneous. The majority of currentsolvent extraction technologies (Interline, Snamprogetti, Cyclon)use propane as a solvent, which has a lower selectivity to undesiredspecies compared with MRD. Moreover propane requires highsolvent–oil ratios which increase energy consumption. Fromeconomical and technological points of view replacing propanewith MRD looks feasible.

Thus, currently the most attractive method for rerefiningused oil could be a combination of MRD-solvent extraction andhydrofinishing, since application of the hydrofinishing step givesproduct oils of high quality independent of the feedstock nature.The MRD-solvent extraction process allows reduced catalystpoisoning without any alkaline treatment of the used oil. Absenceof a need to apply alkali agents makes it possible to regeneratesynthetic and semi-synthetic oils along with mineral oils. Thecomposition of hydroprocessing catalysts could be optimized toincrease catalyst stability and achieve the highest oil conversionand yield.

REFERENCES1 Giovanna FD, Khlebinskaia O, Lodolo A, Miertus S, Compendium of

used oil regeneration technologies. UNIDO, Trieste (2003). Exformhttp://institute.unido.org/documents/M8_LearningResources/ICS/95.%20Compendium%20of%20Used%20Oil%20Regeneration%20Technologies.pdf

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Documents

Technology for rerefining used lube oils applied in Europe: a review