EP0708174A1 - Method and installation for purifying used oils - Google Patents

Abstract

Purification of used oils comprises stages of de-hydration, vacuum distillation, solvent extraction and hydro-treatment. Direct vacuum distillation of the de-hydrated used oil produces a residue and at least one distillate fraction, the residue from the vacuum distillation is submitted to solvent extraction to give a clarified oil and an extraction residue, the clarified oil and oil distillate fraction(s) are stabilised by hydro-treatment. Also claimed is an installation for effecting the treatment.

Description

The present invention relates to a method and an installation for the purification of used oils, that is to say a treatment having the aim of producing at least one oil base which can again be used.

These oils are in particular mineral oils of hydrocarbons, generally of petroleum origin, most often containing various additives such as anti-rust agents, antioxidants, emulsifiers, viscosity additives, etc., oils which after a more or less long use in an internal combustion engine, as lubricating agents, have seen their properties modified in a disadvantageous manner and are loaded with products such as carbonaceous residues, oxidized products, water, unburned hydrocarbons, which has led to their draining.

Used oils contain a multitude of contaminating elements since practically all the groups of the periodic table can be represented, as the example demonstrates below.

In addition to the variety of elements present and the diversity of their contents in the oil, it is necessary to take into account, in order to appreciate the difficulty of the problem to be solved, that each oil has a particular origin therefore is differently contaminated.

Large quantities of complex mixtures of oils have to be treated.

• 1/ Extraction de l'huile usagée au moyen d'un hydrocarbure paraffinique renfermant de 3 à 6 atomes de carbone ou d'un mélange de plusieurs de ces hydrocarbures, suivie de la séparation des phases d'extrait et de raffinat : l'extrait est ensuite débarrassé, par exemple par strippage, de l'hydrocarbure léger qui avait servi à l'extraction.
  Cette extraction est avantageusement précédée d'un traitement par chauffage qui consiste à débarrasser l'huile des fractions légères qu'elle contenait, par exemple eau et essence, par chauffage à une température de distillation inférieure à 200 °C, par exemple 120 à 150°C. D'autres prétraitements connus sont la décantation, la filtration, la centrifugation et la neutralisation.
• 2/ Distillation de l'extrait préalablement débarrassé de l'hydrocarbure léger d'extraction, de manière à séparer au moins une fraction d'huile lubrifiante distillée d'un résidu d'huile lubrifiante non-distillée.
• 3/ Hydrogénation de la fraction distillée.
• 4/ Traitement du résidu de distillation de l'étape (2), au moyen d'un adsorbant, par exemple l'alumine, la bauxite, la silice, une argile, une terre activée ou une silice alumine.

French patent FR 2,301,592 proposes a process for treating these oils which comprises the following essential steps:

• 1 / Extraction of the used oil using a paraffinic hydrocarbon containing 3 to 6 carbon atoms or a mixture of several of these hydrocarbons, followed by the separation of the extract and raffinate phases: the extract is then freed, for example by stripping, of the light hydrocarbon which had been used for the extraction.
  This extraction is advantageously preceded by a heating treatment which consists in ridding the oil of the light fractions which it contained, for example water and petrol, by heating at a distillation temperature below 200 ° C., for example 120 to 150 ° C. Other known pretreatments are decantation, filtration, centrifugation and neutralization.
• 2 / Distillation of the extract previously freed from the light hydrocarbon of extraction, so as to separate at least a fraction of distilled lubricating oil from a residue of non-distilled lubricating oil.
• 3 / Hydrogenation of the distilled fraction.
• 4 / Treatment of the distillation residue from step (2), using an adsorbent, for example alumina, bauxite, silica, clay, activated earth or silica alumina.

Unfortunately, it has been found that the treatment of the residue with an adsorbent results in a loss of oil and therefore a reduction in the yield of the process. In addition, the disposal of these large quantities of polluted adsorbent (most often by incineration) poses environmental problems.

Another process for the regeneration of waste oils uses treatment with sulfuric acid of the cuts obtained during clarification with solvent or distillation under vacuum. These sections, freed from acid sludge, are then treated with adsorbent.

In the two processes described, waste (acid sludge, adsorbents) is produced, the elimination of which requires taking into account the ecological constraints linked to environmental protection. This elimination, storage and treatment is therefore expensive and increases the costs of current processes.

In addition, such treatments with adsorbents and acids may be prohibited in the future.

The applicant proposes here a process and an installation using no acids or adsorbents, with therefore a higher oil recovery yield to produce oils of improved quality meeting the new quality standards, that is to say say oils that may be equivalent to those obtained in a refinery.

In addition, this simple process, requiring a minimum of operations, can be adapted to existing installations.

• . les huiles usagées déshydratées sont directement distillées sous vide pour produire un résidu et au moins une fraction d'huile distillée,
• . le résidu de distillation sous vide est soumis directement à ladite extraction de façon à obtenir une huile dite clarifiée et un résidu d'extraction,
• . la (les) fraction(s) d'huile distillée et l'huile clarifiée sont soumises à un traitement de stabilisation par hydrotraitement.

More specifically, the subject of the invention is a process for the purification of used oils, comprising the steps of dehydration, vacuum distillation, solvent extraction and hydrotreatment, process in which:

• . the dehydrated used oils are directly distilled under vacuum to produce a residue and at least a fraction of distilled oil,
• . the vacuum distillation residue is subjected directly to said extraction so as to obtain a so-called clarified oil and an extraction residue,
• . the distilled oil fraction (s) and the clarified oil are subjected to a stabilization treatment by hydrotreatment.

The description of the invention will more easily be followed from the diagram of the process and of the installation in FIG. 1.

The charge of used oil (s) to be treated which has been freed of the suspended particles beforehand by filtration, for example on a sieve, is introduced into the dehydration zone 2.

The dehydration techniques are those used on most oil regeneration chains.

Usually, after having advantageously preheated the oil in a specially equipped oven, a gentle distillation of the crude oil is carried out so as to remove the water (generally 2 to 4%).

This distillation is carried out at atmospheric pressure or under a slight vacuum so as not to damage the products. The distillation temperature is less than 240 ° C or even less than 200 ° C, for example 120 to 180 ° C, or 120 - 150 ° C.

It is also possible to eliminate at least part of the gasoline (1 to 2%), solvents, glycol, certain derivatives of additives. These eliminated light fractions are symbolized by L in FIG. 1, and the water by E. These fractions L and the water can be discharged together or separately.

The HD dehydrated oil thus obtained is sent directly to a vacuum distillation zone 5, that is to say without undergoing solvent extraction as in the prior art.

This oil charge is brought to an elevated temperature so as to subject it to an appropriate heat treatment so that the oil is not thermally cracked, but that the dispersing additives are destabilized.

By vacuum distillation, there is produced a residue R and at least one fraction of distilled oil D (which can thus be called vacuum distillate).

The vacuum distillation column will advantageously be adjusted in order to obtain at the head a so-called diesel cut (GO), in lateral withdrawal one or more cuts called vacuum distillates and at the bottom a distillation residue. This preferred embodiment is shown in FIG. 1 with the production of two distillates under vacuum.

The diesel cut collected at the head of the column is very rich in chlorine and contains metals, mainly silicon. Its final boiling point is between 280 and 370 ° C.

Vacuum distillates contain very little metal and chlorine.

The distilled fraction could be, for example, a spindle fraction (light oil with viscosity at 40 ° C close to 20.10⁻⁶ m / s) and oil bases for engines such as SSU 100 to 600 oils.

The vacuum residue contains the majority of the metals and metalloids (of the order of 6,000 - 25,000 ppm for example) present in the oil and essentially precipitated polymers. It corresponds to an initial boiling point of 450 to 500 ° C.

The vacuum residue obtained is sent to an extraction zone 9 where it is preferably treated using a paraffinic hydrocarbon containing 3 to 6 carbon atoms or a mixture of several of these hydrocarbons in the liquid state, so as to extract the clarified oil from the residue.

The extraction treatment with light liquid paraffinic hydrocarbon is preferably carried out between 40 ° C. and the critical temperature of the hydrocarbon, under a pressure sufficient to maintain this hydrocarbon in the liquid state. With propane, for example, the preferred temperature is between 45 ° C and the critical temperature of the hydrocarbon. We will seek to obtain the largest possible temperature gradient in the extraction zone. It is for this reason that the inlet temperature will be low (below 70 ° C, and better still below 60 ° C). The temperature gradient is preferably greater than 20 ° C, and better still at least 25 ° C). The liquid hydrocarbon / oil volume ratio is from 2: 1 to 30: 1, preferably 5: 1 to 15: 1. Propane is the preferred hydrocarbon.

In general, the residue must therefore be cooled before being introduced into the extraction zone. It is never heated between vacuum distillation and extraction. We then say that it is sent "directly" to extraction.

The contacting of the residue under vacuum with the light paraffinic hydrocarbon is generally carried out continuously in a column (extractor) from which a mixture of paraffinic hydrocarbon and clarified oil is drawn off on the one hand, and on the other hand at the bottom an extraction residue R 'entraining part of said paraffinic hydrocarbon.

Advantageously, the quantity of solvent (paraffinic hydrocarbon) injected into the extractor is divided into two equal or unequal parts. A quantity is used to dilute the charge and to regulate the injection temperature of the mixture, the other part, injected directly into the column, is used to adjust the temperature at the bottom of the column and also to continue extracting the oil trapped in the residue.

This process is very effective due to the selective dissolution of the oil in the paraffinic hydrocarbon, and the precipitation of an extremely concentrated residue at the bottom of the column. This treatment is very effective in terms of the quality and yield of the viscous oil recovered (Bright Stock; viscosity at 100 ° C = 30 x 10⁻⁶ to 35 x 10⁻⁶ m / s).

The light paraffinic hydrocarbon is separated from the clarified HC oil and can then be recycled to the extraction zone. For example, in a conventional embodiment where the solvent is separated from the oil by vaporization of the head mixture of the extractor, the light hydrocarbon is separated from the oil by expansion and reheating followed by steam entrainment. clarified. The light hydrocarbon is, after cooling, compression and condensation, advantageously recycled for a new extraction.

According to another embodiment, the solvent is recovered under supercritical conditions as described in patent FR-2,598,717, the teaching of which is included. In this case, the extraction zone operates under a higher supercritical pressure than in the first embodiment (P = 35 or 40 - 70 bar instead of 30 - 40 bar). The separation of the phases is then obtained by heating, without vaporization or condensation. The solvent is then recycled under supercritical pressure. The advantage of these supercritical conditions is that it eliminates the vaporization and vapor condensation operations necessary in the case of conventional conditions for recovering the solvent.

The extractor base mixture contains the residue part precipitated in the light hydrocarbon. This mixture has a fairly low viscosity because of the amount of light hydrocarbon it contains. Once the light hydrocarbon has been removed, its handling becomes very delicate because of the high viscosity. To overcome this drawback, the extraction residue containing solvent withdrawn from the bottom of the extractor can be mixed with a viscosity step-down. The assembly after expansion is, for example, heated and stripped with steam. The light hydrocarbon after compression and condensation is recycled to the extraction column. The residue completely freed from the solvent can be recovered as fuel or mixed with bitumens.

The distilled oil fraction (s) and the clarified oil HC are sent (alone or as a mixture) to a hydrotreatment zone 12 where they are treated with hydrogen in the presence of at least one catalyst for finish purifying them and improving their qualities for better recovery.

This treatment makes it possible to obtain lubricating oils in accordance with the specifications without having to use treatment with soil and / or treatment with sulfuric acid. These lubricating oils have very good thermal stability and good light stability. The hydrotreatment catalyst (s) have an extended service life because the products having undergone the pretreatment operations are well purified.

The catalyst is a hydrotreating catalyst containing at least one oxide or sulphide of at least one group VI metal and / or at least one group VIII metal, such as molybdenum, tungsten, nickel, cobalt, a support, for example alumina, silica-alumina or a zeolite.

A preferred catalyst is a catalyst based on nickel and molybdenum sulfides supported on alumina.

• vitesse spatiale : 0,1 à 10 volumes de charge liquide par volume de catalyseur et par heure,
• température entrée réacteur : entre 250 et 400 °C, de préférence entre 280 et 370 °C,
• pression au réacteur : de 5 à 150 bar, de préférence de 15 à 100 bar,
• avantageusement recyclage H₂ pur : de 100 à 2 000 Nm³/m³ de charge.

The operating conditions for hydrotreatment are as follows:

• space velocity: 0.1 to 10 volumes of liquid charge per volume of catalyst and per hour,
• reactor inlet temperature: between 250 and 400 ° C, preferably between 280 and 370 ° C,
• reactor pressure: from 5 to 150 bar, preferably from 15 to 100 bar,
• advantageously pure H₂ recycling: from 100 to 2,000 Nm³ / m³ of charge.

Because we were able to obtain during previous treatments distillates under vacuum and a "Brigth Stock" cut from clarified oil well purified (the residual metals are less than 5 and 20 ppm respectively), the hydrotreatment is of quality .

A final distillation allows, if necessary, to adjust the cutting points.

The diesel fraction obtained at the end of the vacuum distillation can also be hydrotreated in order to remove the chlorine and to lower the sulfur content. It is very advantageous to mix the diesel fraction with the light fractions L obtained on dehydration by atmospheric distillation.

This hydrotreatment is preferably carried out with the catalysts used for the treatment of the distillate (s) under vacuum and the clarified oil. The qualities of diesel obtained at the end of this hydrotreatment make it possible to pass all the specifications successfully and allows the incorporation of this cut into fuel storage.

The treatment according to the present invention carried out with hydrotreatment makes it possible to maintain a good level of activity of the catalyst.

• l'huile ou les huiles, à partir de la fraction (des fractions) d'huile distillée correspondantes,
• le "Bright Stock", à partir de la fraction d'huile clarifiée,
• le mélange gaz, hydrocarbures légers, contenant l'hydrogène de purge,
• éventuellement, une coupe essence-gazole, à partir de la coupe gazole et des fractions légères contenant l'essence.

At the end of the hydrotreatment (possibly accompanied by a finishing distillation), it is obtained, for each of the fractions treated:

• the oil or oils, from the corresponding fraction (fractions) of distilled oil,
• "Bright Stock", from the clarified oil fraction,
• the gas, light hydrocarbon mixture containing the purge hydrogen,
• optionally, a petrol-diesel cut, from the diesel cut and light fractions containing petrol.

The qualities of oils obtained comply with the required specifications. They have very satisfactory thermal and light stability.

There is a very low loss of viscosity compared to the charge of used oils and a slight deterioration of the pour point in some cases.

The metal content is less than 5 ppm, and the chlorine content less than 5 ppm and most often undetectable.

The content of aromatic polynuclear compounds (PNA) is most often of the order of that of base oils obtained by hydrorefining (of the order of 0.2-0.5% by weight), it can be equal to that of oils refined with solvent (furfurol for example), that is to say approximately 1.5% by weight.

• une zone (2) de déshydratation munie d'une canalisation (1) d'introduction de la charge d'huile usagée, d'une canalisation (3) pour la sortie de l'eau et d'une canalisation (4) pour l'évacuation de l'huile déshydratée,
• une canalisation (4) qui évacue de la zone (2) de déshydratation l'huile déshydratée et l'amène directement dans la zone (5) de distillation sous vide,
• une zone (5) de distillation sous vide dans laquelle débouche la canalisation (4) et munie d'au moins une canalisation (7) pour l'évacuation de la (des) fraction(s) d'huile distillée, et d'au moins une canalisation (8) pour l'évacuation du résidu sous vide,
• une zone (12) d'hydrotraitement munie d'au moins une canalisation (7, 10, 13) pour l'introduction de la coupe à traiter, d'au moins une canalisation pour l'évacuation de la coupe traitée (16, 17) d'au moins une canalisation (14) pour amener l'hydrogène, et d'au moins une canalisation (15) pour la sortie des gaz,
• une zone d'extraction (9) munie d'une canalisation (18) pour l'introduction du solvant, d'une canalisation (8) pour amener directement le résidu de la zone (5) de distillation sous vide à la zone (9), d'une canalisation (11) pour l'évacuation du résidu d'extraction et d'une canalisation (10) pour la sortie de l'huile clarifiée.

The subject of the invention is also an installation for implementing the method described, which comprises:

• a dehydration zone (2) provided with a pipe (1) for introducing the charge of used oil, a pipe (3) for the outlet of the water and a pipe (4) for the '' evacuation of dehydrated oil,
• a pipe (4) which evacuates the dehydrated oil from the dehydration zone (2) and brings it directly into the vacuum distillation zone (5),
• a vacuum distillation zone (5) into which the pipe (4) opens and provided with at least one pipe (7) for the evacuation of the fraction (s) of distilled oil, and at least least one pipe (8) for evacuating the residue under vacuum,
• a hydrotreating zone (12) provided with at least one pipe (7, 10, 13) for the introduction of the cut to be treated, with at least one pipe for the evacuation of the treated cut (16, 17 ) at least one line (14) for supplying the hydrogen, and at least one line (15) for the outlet of the gases,
• an extraction zone (9) provided with a pipe (18) for the introduction of the solvent, a pipe (8) for directly bringing the residue from the vacuum distillation area (5) to the area (9 ), a line (11) for the evacuation of the extraction residue and a line (10) for the outlet of the clarified oil.

Advantageously, the installation comprises, as zone (2), an atmospheric distillation or a light vacuum with separation of the light fraction (s) L containing the gasoline by a pipe (13). Advantageously, it also includes a pipe (6) for evacuating the diesel cut from the vacuum distillation zone (5).

The diesel, distilled oil, clarified oil fractions can be treated directly by hydrotreatment in zone (12) (representation of FIG. 1), it being understood that they are treated separately. Advantageously, they will be stored separately and processed by campaign.

The hydrogen is introduced into the hydrotreatment zone (12) directly into the reactor (as in FIG. 1) but it can be introduced with the feed to be treated. The invention includes this possibility.

On the vacuum evacuation pipe (8), a heat exchanger is advantageously arranged to cool the residue.

After extraction, that is to say at the level of zone (9), a means is advantageously arranged for the separation of the solvent from the clarified oil. This means is preferably a means of vaporization. It is advantageously composed of at least one pressure reducer, a heating means and a steam drive device (stripper).

The recovered solvent then preferably passes through a heat exchanger, a compressor and a condenser before being recycled for extraction by a suitable pipe which connects said separation means and the extraction zone (9).

In another embodiment, it is arranged at the level of the zone (9) under supercritical conditions, a heating means making it possible to separate the solvent and a pipe for recycling the solvent to the zone (9).

We illustrate the present invention by taking as an example an oil having been dehydrated, the analysis of which is as follows: Characteristics Dehydrated oil Density at 15 ° C 0.892 ASTM D1500 color 8 + Pour point ° C - 18 Viscosity at 40 ° C * cSt 102.11 Viscosity at 100 ° C * cSt 11.7 Viscosity index 102 Total nitrogen ppm 587 Suffers % weight 0.63 Chlorine ppm 280 Conradson carbon % weight 1.56 Sulfated centers % weight 0.9 Phosphorus ppm 530 Flash point open vase ° C 230 Neutralization index mg KOH / g 0.92 Metals (total) ppm 3,445 Ba ppm 10 It ppm 1,114 Mg ppm 324 B ppm 16 Zn ppm 739 P ppm 603 Fe ppm 110 Cr ppm 5 Al ppm 20 Cu ppm 18 Sn ppm 1 Pb ppm 319 V ppm 1 Mo ppm 3 Yes ppm 31 N / A ppm 129 Or ppm 1 Ti ppm 1 * The viscosity is expressed in cSt (centistock) and 1 cSt = 10⁻⁶ m / s.

The water removed by atmospheric distillation represents 4% by weight of the charge and the light fraction L 2.4% by weight.

The dehydrated oil (93.6% of the charge) is sent to the vacuum distillation unit: in the example chosen, we have grouped the two distillates from the side draws. The 1 + 2 distillates correspond to boiling points between 280 ° C and 565 ° C. The 1 + 2 distillates are sent to the hydrotreatment unit, the vacuum residue is sent to the solvent clarification unit (extraction zone (9)). The analysis of products from vacuum distillation in our example is as follows: Characteristics DSV Cup (1 + 2) RSV Cup Density 15 ° C 0.8768 0.9302 ASTM D1500 color 8 Black Pour point ° C - 9 - 15 Viscosity at 40 ° C * cSt 49.39 959.5 Viscosity at 100 ° C * cSt 7.12 55.96 Viscosity index 101 111 Total nitrogen ppm 180 1,535 Sulfur % weight 0.47 1.00 Chlorine ppm 45 830 Phosphorus ppm 15 1,740 Conradson carbon % weight 0.08 5 Flash point open vase ° C 231 283 Sulphated ash % weight 0.005 3 Sediments ppm 0.05 0.6 Neutralization index Total acid mg KOH / g 0.14 Strong acid mg KOH / g 0 Based mg KOH / g 0.24 Metals (total) ppm ≈ 11 11,444 Ba ppm <1 30 It ppm <1 3,711 Mg ppm <1 1,077 B ppm <1 51 Zn ppm <1 2,462 P ppm 6 1,995 Fe ppm <1 365 Cr ppm <1 15 Al ppm <1 64 Cu ppm <1 59 Sn ppm <1 22 Pb ppm <1 1,060 V ppm <1 2 Mo ppm <1 7 Yes ppm 3 95 N / A ppm 2 425 Or ppm <1 2 Ti ppm <1 2 * 1cSt = 10⁻⁶m / s;

The bottom cut (vacuum residue) obtained during vacuum distillation is sent to the solvent extraction unit.

The operating conditions applied during this operation are as follows: Total solvent oil report: 8/1 Light hydrocarbon: propane Extractor head temperature: 85 ° C Extractor foot temperature: 55 ° C Pressure: 39 bar.

After this extraction, the light hydrocarbon is separated from the residue by vaporization. The residue obtained is "fluxed" (mixed with dehydrated oil or with a viscosity-lowering hydrocarbon) and can be used as fuel or used as a binder in road bitumens.

The clarified oil is separated from the light hydrocarbon by vaporization to give the Bright Stock (BS) cut.

Characteristics RSV B.S. clarified at C3 Density 15 ° C 0.9302 0.895 ASTM D1500 color Black 8 + Pour point ° C - 15 - 9 Viscosity at 40 ° C * cSt 959.5 377 Viscosity at 100 ° C * cSt 55.96 25.40 Viscosity at 150 ° C cSt Viscosity index 111 89 Total nitrogen ppm 1,535 375 Sulfur % weight 1.00 0.786 Chlorine ppm 830 20 Phosphorus ppm 1,740 15 Conradson carbon % weight 5 0.60 Flash point open vase ° C 283 332 Sulphated ash % weight 3 <0.005 Sediments ppm 0.6 <0.05 Neutralization index Total acid mg KOH / g 0.3 Strong acid mg KOH / g 0.0 Based mg KOH / g 0.55 Metals (total) ppm 11,444 ≈ 19 Ba ppm 30 <1 It ppm 3,711 1 Mg ppm 1,077 <1 B ppm 51 1 Zn ppm 2,462 1 P ppm 1,995 <1 Fe ppm 365 <1 Cr ppm 15 <1 Al ppm 64 <1 Cu ppm 59 <1 Sn ppm 22 6 Pb ppm 1,060 <1 V ppm 2 <1 Mo ppm 7 <1 Yes ppm 95 7 N / A ppm 425 3 Or ppm 2 <1 TI ppm 2 <1 * 1cSt = 10⁻⁶m / s;

The mixture of distillates under vacuum 1 + 2 and the oil (Bright Stock) are sent respectively (separately) to the hydrotreating unit on a catalyst containing nickel sulfide, molybdenum sulfide and an alumina support.

The operating conditions are as follows: Temperature : 300/280 ° C Partial hydrogen pressure: 50 bar Residence time : 1 hour Hydrogen recycling 380 Nm³ / m³ of load.

The qualities of the products obtained at the end of this hydrotreatment are compared with those of respective fillers in the table below: Characteristics DSV Cup (1 + 2) DSV Cup (1 + 2) hydrogenated BS Cup Hydrogenated BS cup Density 15 ° C 0.8768 0.872 0.895 0.893 ASTM D1500 color 8 - 1 - 8 + 2.5 Pour point ° C - 9 - 6 - 9 - 6 Viscosity at 40 ° C * cSt 49.39 47.39 377 373.48 Viscosity at 100 ° C * cSt 7.12 7.00 25.40 25.10 Viscosity index 101 104 89 88 Total nitrogen ppm 180 65 375 217 Sulfur % weight 0.47 0.182 0.786 0.443 Chlorine ppm 45 0 20 0 Phosphorus ppm 15 0 15 0 Conradson carbon % weight 0.08 0.014 0.60 0.39 Flash point open vase ° C 231 220 332 309 Neutralization index Total acid KOH / g mg 0.14 0.06 0.3 0.02 Strong acid KOH / g mg 0.0 0.0 0.0 0.0 KOH base / g mg 0.24 0.13 0.55 0.36 Aromatic polycyclics % weight <0.5 <0.5 Metals (total) ppm 11 1 19 1 Ba ppm 0 0 0 0 It ppm 0 0 1 0 Mg ppm 0 0 0 0 B ppm 0 0 1 0 Zn ppm 0 0 1 0 P ppm 6 0 0 0 Fe ppm 0 0 0 0 Cr ppm 0 0 0 0 Al ppm 0 0 0 0 Cu ppm 0 0 0 0 Sn ppm 0 0 6 0 Pb ppm 0 0 0 0 V ppm 0 0 0 0 Mo ppm 0 0 0 0 Yes ppm 3 0 7 1 N / A ppm 2 1 3 0 Or ppm 0 0 0 0 Tl ppm 0 0 0 0 * 1 cSt = 10⁻⁶ m / s.

The products obtained after hydrotreating are characterized by a reduction in the content of heavy aromatics, a significant reduction in the sulfur content, and by a total elimination of chlorine and metals. The viscosity index of these oil bases is maintained or improved, the stability in the presence of heat or light is very good.

The extraction unit is therefore very well suited for treating the residue cut under vacuum and moreover it requires an investment divided by 3 compared to the investment of a total oil clarification installation after dehydration, since the unit capacity is reduced to about a third of that required in the prior art.

It has been observed that extraction of the oil after dehydration does not make it possible to obtain as good a quality of oil: the metals contained in the clarified oil are in an amount greater than 300 ppm.

It can then be argued that the extraction is all the better as the medium treated is concentrated in metals and heavy molecules.

The molecules containing the metals (impurities) easily precipitate in the solvent medium, the high concentration of metals (degraded additives) makes it possible to have insoluble micelles which will increase while their residence time in the column and by difference in density fall to the bottom of the extractor.

The present invention, which has demonstrated and exploited this effect, makes it possible to make the most of all the products contained in the collected used oil. The yield of recoverable products is close to 99% compared to the quantity of hydrocarbon contained in the collected oil. There are no liquid or solid products to incinerate as is the case in all other processes. The residue leaving the extraction is itself recoverable.

Claims (14)

Process for the purification of used oils, comprising the stages of dehydration, vacuum distillation, solvent extraction and hydrotreatment, process characterized in that: . the dehydrated used oils are directly distilled under vacuum to produce a residue and at least a fraction of distilled oil, . the vacuum distillation residue is subjected directly to said extraction so as to obtain a so-called clarified oil and an extraction residue, . the distilled oil fraction (s) and the clarified oil are subjected to a stabilization treatment by hydrotreatment. Process according to claim 1, characterized in that the waste oils are dehydrated by atmospheric distillation at a temperature below 240 ° C. Method according to one of the preceding claims, characterized in that the vacuum distillation residue has an initial boiling point of between 450 and 500 ° C. Method according to one of the preceding claims, characterized in that the vacuum distillation produces a so-called diesel fraction with a final boiling point of between 280 and 370 ° C. Method according to one of the preceding claims, characterized in that the extraction is carried out using at least one paraffinic hydrocarbon containing 3 to 6 carbon atoms, at a temperature between 40 ° C and the critical temperature of the hydrocarbon, under sufficient pressure to maintain the hydrocarbon in the liquid state, and with a hydrocarbon / oil volume ratio of 2: 1 and 30: 1. Method according to one of the preceding claims, characterized in that the extraction is carried out with propane. Method according to one of the preceding claims, characterized in that the fraction resulting from the extraction containing the clarified oil also containing the solvent is subjected to a vaporization so as to separate the solvent which is recycled in extraction. Method according to one of claims 1 to 6, characterized in that the solvent is separated from the clarified oil under supercritical conditions and that it is recycled by extraction under supercritical pressure. Method according to one of the preceding claims, characterized in that the extraction residue is mixed with a viscosity step-down. Method according to one of the preceding claims, characterized in that the diesel fuel cut (s) is also subjected to hydrotreatment. Method according to one of the preceding claims, characterized in that the hydrotreatment takes place under hydrogen, in the presence of a catalyst having a support and containing at least one oxide or a sulphide of at least one group VI metal and / or at least one group VIII metal, at a temperature of 250-400 ° C, a pressure of 5 - 150 bar, a space speed of 0.1-10h⁻¹. Installation for implementing the method according to one of claims 1 to 11, comprising: . a dehydration zone (2) provided with a pipe (1) for introducing the charge of used oil, a pipe (3) for the outlet of the water and a pipe (4) for the '' evacuation of dehydrated oil, . a vacuum distillation zone (5) into which the pipe (4) opens and provided with at least one pipe (7) for the evacuation of the fraction (s) of distilled oil, and at least least one pipe (8) for evacuating the residue under vacuum, . a hydrotreating zone (12) provided with at least one pipe (7, 10, 13) for the introduction of the cut to be treated, with at least one pipe for the evacuation of the treated cut (16, 17 ), at least one line (14) for supplying the hydrogen, and at least one line (15) for the outlet of the gases, . a solvent extraction zone (9), said installation being characterized in that: . a pipe (4) evacuates from the dehydration zone (2) the dehydrated oil and brings it directly into the vacuum distillation zone (5), . the extraction zone (9) is provided with a line (18) for the introduction of the solvent, a line (8) for directly bringing the residue from the vacuum distillation zone (5) to the zone ( 9), a line (11) for the evacuation of the extraction residue and a line (10) for the outlet of the clarified oil. Installation according to claim 12 characterized in that the zone 2 for dehydration by distillation is provided with a pipe (13) for the outlet of the light fraction containing the gasoline and that a pipe (6) evacuates from the area (5 ) vacuum distillation of the diesel cut. Installation according to one of claims 12 or 13, characterized in that, at the level of the zone (9), is arranged a means for the separation of the solvent from the clarified oil, and a solvent recycling pipe connects said means separation and extraction zone (9).

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