EP0708174B1 - Method and installation for purifying used oils - Google Patents

Description

The present invention relates to a method and an installation for the purification of used oils, i.e. a treatment intended to produce at least one base oil usable again.

These oils are in particular mineral oils of hydrocarbons, generally of petroleum origin, most often containing various additives such as agents anti-rust, antioxidants, emulsifiers, viscosity additives, etc., oils which after more or less long use in an internal combustion engine, as agents lubrication, have had their properties adversely changed and have loaded with products such as carbonaceous residues, oxidized products, water, hydrocarbons not burnt, which led to drain them.

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 oil, it to appreciate the difficulty of the problem to be solved, take into account that each oil has a particular provenance so is differently contaminated.

We thus have to deal with large quantities of complex mixtures of oils.

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, therefore a reduction in the yield of the process. Moreover, the elimination of these significant quantities of polluted adsorbent (by incineration the most often) poses environmental problems.

Another process for regenerating used oils uses acid treatment sulfuric sections obtained during clarification with solvent or distillation under empty. These sections, freed from acid sludge, are then treated with adsorbent.

In the two processes described, waste (acid sludge, adsorbents) is produced, elimination 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, therefore with a higher oil recovery yield to produce oils of improved quality meeting the new quality standards, that is to say oils which may be equivalent to those obtained in a refinery.

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

Furthermore, it is known from document FR-A-2,414,549 to treat waste oils by subjecting them to the following successive stages: dehydration, solvent extraction. heating, vacuum distillation to produce light and heavy oils (residue), heating the residue, solvent extraction of the heated residue to produce an extracted oil, hydrotreating of light and extracted oils.
Document FR-A-2,353,631 also teaches the treatment of waste oils by dehydration, vacuum distillation and solvent extraction of distilled oils, but the residue is not treated (fuel oil).

• l'huile usagée déshydratée est directement distillée 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 ce 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 a used oil, comprising the stages of dehydration, of vacuum distillation. solvent extraction and hydrotreatment, process in which:

• the dehydrated used oil is 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 from the installation figure 1.

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

Dehydration techniques are those used on most regeneration chains of oils.

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

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

You can also remove at least part of the gasoline (1 to 2%), solvents, glycol, certain additive derivatives. 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 5, that is to say without undergoing solvent extraction as in the art prior.

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

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

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

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 of viscosity at 40 ° C close to 20.10 ^-6 m ² / s) and engine oil bases such as SSU 100 to 600 oils.

The vacuum residue contains the majority of metals and metalloids (around 6,000 - 25,000 ppm for example) present in oil and mainly polymers rushed. 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 treated with preferably by means of 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 carried out preferably between 40 ° C and the critical temperature of the hydrocarbon, under pressure sufficient to maintain this hydrocarbon in the liquid state. With propane, by example, the preferred temperature is between 45 ° C and the critical temperature of the hydrocarbon. We will seek to obtain the largest temperature gradient possible in the extraction area. It is for this reason that the inlet temperature will be low (below 70 ° C, and better below 60 ° C). The gradient of temperature is preferably higher than 20 ° C, and better still at least 25 ° C). The liquid hydrocarbon / oil volume ratio is 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 zone extraction. It is never heated between vacuum distillation and extraction. One says while it is sent "directly" to the extraction.

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

Advantageously, the amount 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 adjust the injection temperature of the mixture, the other part, injected directly in the column, is used to adjust the temperature at the bottom of the column and also continue to extract 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 ² / s).

The light paraffinic hydrocarbon is separated from the clarified oil HC and can then be recycled to the extraction area. For example, in a classic embodiment where the solvent is separated from the oil by vaporization of the extractor head mixture on separates, by expansion and reheating followed by steam training, the hydrocarbon light clarified oil. 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 that case, the extraction zone operates under a higher supercritical pressure than in the first realization (P = 35 or 40 - 70 bar instead of 30 - 40 bar). The separation phases is then obtained by heating, without vaporization or condensation. The solvent is then recycled under supercritical pressure. The advantage of these conditions supercritical is to eliminate the vaporization and condensation operations of vapors necessary in the case of conventional conditions to recover the solvent.

The extractor base mixture contains the residue precipitated in the hydrocarbon lightweight. This mixture has a fairly low viscosity due to 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 at the bottom of the extractor can be mixed with a step-down viscosity. The assembly after expansion is, for example, heated and stripped with steam. The light hydrocarbon after compression and condensation, is recycled to the column extraction. The residue completely freed from the solvent can be recovered in the form of fuel or mixed with bitumen.

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

This treatment makes it possible to obtain lubricating oils in accordance with the specifications. without resorting to soil treatment and / or acid treatment sulfuric. These lubricating oils have very good thermal stability and good light stability. Hydrotreatment catalyst (s) have a lifetime prolonged because the products having undergone the pre-treatment operations are well purified.

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

A preferred catalyst is a catalyst based on nickel sulfides and molybdenum 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 recycling pure H ₂ from 100 to 2,000 Nm ³ / m ³ of charge.

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

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

The diesel fraction obtained after vacuum distillation can also be hydrotreated to remove chlorine and lower the sulfur content. We can very advantageously mix the diesel cut with the light fractions L obtained at the dehydration by atmospheric distillation.

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

• 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 present very satisfactory thermal and light stability.

There is a very small loss of viscosity compared to the charge of used oils and slight alteration 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 that of the base oils obtained by hydrorefining (of the order of 0.2-0.5% weight), it can be equal to that of refined solvent oils (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 introducing the cut to be treated, at least one pipe for discharging 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) a distillation atmospheric or under light vacuum with separation of the light fraction (s) L containing petrol by a pipe (13). Advantageously, it also comprises a pipe (6) for evacuating the diesel cut from the distillation zone (5) under vacuum.

The diesel, distilled oil and clarified oil fractions can be processed 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.

Hydrogen is introduced into the hydrotreating zone (12) directly into the reactor (as in Figure 1) but it can be introduced with the load 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), it is advantageously disposed means for separating the solvent from the clarified oil. This means is preferably a means of vaporization. It is advantageously composed of at least one regulator, one heating means and a steam drive device (stripper).

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

In another embodiment, it is arranged in the area (9) under conditions supercritical, a heating means to separate the solvent and a pipe to recycle the solvent to 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 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 hydrotreating 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

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 oil solvent ratio 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 hydrocarbon viscosity reducer) 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 BS 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

The mixture of vacuum distillates 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 Nm ³ / m ³ 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

The products obtained after hydrotreatment are characterized by a reduction heavy aromatics content, a significant decrease in sulfur content, and by a total elimination of chlorine and metals. The viscosity index of these bases of oils is maintained or improved, 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 for the more it requires an investment divided by 3 compared to the investment of a total oil clarification installation after dehydration, since the capacity to the unit is reduced to about a third of that required in the prior art.

It has been observed that an extraction of the oil after dehydration does not allow 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 grow in size as they grow stay in the column and by density difference fall to the bottom of the extractor.

The present invention, which has demonstrated and exploited this effect, makes it possible to enhance the maximum all the products contained in the used oil collected. The yield in recoverable products is close to 99% compared to the amount of hydrocarbon contained in the oil collected. 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)

1. A process for purifying spent oil, comprising the steps of dehydration, vacuum distillation, solvent extraction and hydrotreatment, in which:

   the dehydrated spent oil is directly vacuum distilled to produce a residue and at least one distilled oil fraction;

   the vacuum distillation residue directly undergoes said extraction to obtain a clarified oil and an extraction residue;

   the distilled oil fraction(s) and the clarified oil are stabilised by hydrotreatment.
2. A process according to claim 1, characterised in that the spent oil is dehydrated by atmospheric distillation at a temperature of less than 240°C.
3. A process according to claim 1 or claim 2, characterised in that the vacuum distillation residue has an initial boiling point in the range 450°C to 500°C.
4. A process according to any one of the preceding claims, characterised in that vacuum distillation produces a gas oil cut with a final boiling point in the range 280°C to 370°C.
5. A process according to any one of the preceding claims, characterised in that extraction is carried out using at least one paraffinic hydrocarbon containing 3 to 6 carbon atoms, at a temperature of between 40°C and the critical temperature of the hydrocarbon, at a pressure which is sufficient to maintain the hydrocarbon in the liquid state, and with a hydrocarbon/oil volume ratio in the range 2:1 to 30:1.
6. A process according to any one of the preceding claims, characterised in that extraction is carried out with propane.
7. A process according to any one of the preceding claims, characterised in that the fraction from the extraction step, containing the clarified oil and containing the solvent, is vaporised to separate the solvent which is recycled to the extraction step.
8. A process according to any one of claims 1 to 6, characterised in that the solvent is separated from the clarified oil under supercritical conditions and is recycled to the extraction step at a supercritical pressure.
9. A process according to any one of the preceding claims, characterised in that the extraction residue is mixed with a viscosity reducing agent.
10. A process according to any one of the preceding claims, characterised in that the gas oil cut(s) also undergoes hydrotreatment.
11. A process according to any one of the preceding claims, characterised in that hydrotreatment is carried out in hydrogen, in the presence of a catalyst having a support and containing at least one oxide or sulphide of at least one metal from group VI and/or at least one metal from group VIII, at a temperature of 250°C to 400°C, a pressure of 5 to 150 bar, and a space velocity of 0.1 to 10 h^-1.
12. A plant for carrying out the process according to any one of claims 1 to 11, comprising:

    a dehydration zone (2) provided with an introduction line (1) for the spent oil feed, a line (3) for removal of water and a line (4) for evacuating dehydrated oil;

    a vacuum distillation zone (5) into which line (4) opens and which is provided with at least one line (7) for evacuating the distilled oil fraction(s), and at least one line (8) for evacuating vacuum residue;

    a hydrotreatment zone (12) provided with at least one line (7, 10, 13) for introducing a cut to be treated, at least one line (16, 17) for evacuating a treated cut, at least one line (14) for supplying hydrogen, and at least one line (15) for removing gas;

    a solvent extraction zone (9);

       said plant being characterised in that

    - a line (4) evacuates dehydrated oil from zone (2) and brings it directly to vacuum distillation zone (5);

    - extraction zone (9) is provided with a line (18) for introducing solvent, a line (8) for supplying the residue from vacuum distillation zone (5) to zone (9), a line (11) for evacuating extraction residue and a line (10) for removal of clarified oil;
13. A plant according to claim 12, characterised in that zone 2 for dehydration by distillation is provided with a line (13) for removing a light fraction containing petrol and in that a line (6) evacuates the gas oil cut from the distillation zone (5).
14. A plant according to any one of claims 12 or 13, characterised in that a means is located at zone (9) for separating the solvent from the clarified oil, and a solvent recycling line connects said separating means to the extraction zone (9).

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